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September/October 1981 Volume1, Number 5 $2.50 (USA) 
£1.20 (UK) 


Reviews and Resources: Games: 
e 16K RAM Schematic e Cannonade 
e Hints and Tips for the ZX81 e Robot Composer 
e QS Soundboard e Defuse 
e Hangman 
e Motorcycle Race 
=- Graphics and Math: Programming: 
e GRA+PICS | e PEEK and POKE 
e Prime Numbers e READ on the ZX80 
e Great Circle Route e Key and Token Use 
e ZX80/1 As Fortune Cookie 


— 


SYNTAX ZX80- 


A PUBLICATION OF THE HARVARD GROUP 


SYNTAX ZX80 is a monthly newsletter exclusively 
for ZX80 and MicroAce owners. We bring you 
news, reviews and applications for your computer, 
plus technical notes for circuit-builders. SYNTAX 
also provides a forum for thousands of users to 
share advice and problems about programs and 
vendors. We bring you timely updates about new 
hardware, software and books. And we cover all the 
Sinclair-MicroAce computers, including the new ZX81. 

At SYNTAX we emphasize practicality. You can 
apply our suggestions even if you aren’t sure at first 
why they work, because we give you complete instruc- 
tions. Text is clear and easy to understand. SYNTAX 
readers already know about: 

e An automatic phone-dialer they can put to- 
gether in a few hours 

e Syntactic Sums™ to check input for errors 

e Printing characters four times normal size 

e Programs to explore computer memory 

e Cassette eavesdropping to locate files on 
tape and simplify loading 

e How to build their own external additional 
RAM | 

e How to add an 8212 I/O chip to control 
external devices from their computers 

And SYNTAX readers like what they get every 
month. Subscribers know they can depend on us. 

After receiving only three issues of 
SYNTAX ZX80, I find that I anxiously 
await the next issue... keep up the 
good work! 

Martin Irons 

Goshen, NY 
Congratulations on the brass-tacks, down- 
to-earth approach of your newsletter. Pil 
be looking forward to future issues. 

Otis Imboden 

Washington, DC 

Many readers get their first issue and immediately 
order the back issues — more proof that they like 
what they see. 


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Make checks payable to: 
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What’s special about our publication? Just look 
through one issue. We work hard to bring you a 
quality newsletter. We strive to print useful programs 
of above-average accuracy. As any computer 
magazine editor can tell you, program listing 
accuracy is tough to achieve, but we boost our 
average with every issue. We test each program to 
make sure it works, it fits in the designated RAM, 
and it runs when you follow the directions. We print 
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The magazine for Sinclair users 


— i | 


September/October 1981 


DEPARTMENTS 
TT P 
Glitchoidz Report. 
SYNC Notes............0.000 0000000 eee, Grosjean 
Perceptions. 0.0.0.0... eee, Ornstein 


A ROM Munching Session 


Puzzles and Problems....................... Townsend 
The, Plumb 
Kitchen SYNC............... Groupe, Tardiff, Zatkovich 


GRAPHICS AND MATH 


GRALbICS 0000s Keller 
Geometry on the ZX80/1 8K 


Examining Prime Numbers.................... Repicky 
Two programs 


The Great Circle Route........................ Dawson 
How far from here to there? 


The ZX80/1 As Fortune Cookie.............. Breighner 
Construct your hexagram 


PROGRAMMING 


The PEEK Function and the POKE Command... .Logan 
Fourth in a series 


Staff 


24 


Index to Advertisers 


Volume 1, Number 5 


Machine Language Teaches the 
ZX80 to EA... ENN NNN anes Kennedy 
What is READing? 


Using Key and Token Expressions........... McDaniel 
Tips on byte saving 


GAMES AND PROGRAMS 


Cannonade.................... 00. cece eee Nisbet 
Infiltration under fire 


Robot CGomposer .......... aaua aaa aaaea aaa. Bridges 
Refining the Sinclair music 


Defuse....................... ee e Ate Fowkes 
The race against the clock 


Hangman. 00.0... cee Fowkes 
An old favorite battle of wits 


Motorcycle Race......................... Van Workum 
Mud, gravel, and spills 


REVIEWS AND RESOURCES 
Schematic for Sinclair 16K RAM Pack........ 


Hints and Tips for the ZX81................ Wren-Hilton 
Software review 


The “Q S Sound Board” for the ZX80/81 ` .Wren-Hilton 
Hardware review 


Resources....... 


TE E EN E E E RENE E E E E NEE E E E E E E NEE E NEE E NEE NEE E E E EE 


DEE FEELENER EE 


Publisher/Editor-in-Chief 
Editorial Director 
Managing Editor 
Associate Editor 
Secretary 

Production Manager 

Art Director 

Assistant Art Director 
Typesetters 


Financial Coordinator 
Bookkeeper 
Customer Service 
Order Processing 
Circulation 


MEMBER 


September/October 


David H. Ahl 
George Blank 
Paul Grosjean 

David Lubar 
Elizabeth Magin 
Laura MacKenzie 
Susan Gendzwil 
Diana Negri 

Jean Ann Vokoun 
Maureen Welsh 
William L. Baumann 
Patricia Kennelly 
Ralph Lovery 
Ruth Coles 
Frances Miskovich 
Dorothy Staples 
Carol Vita 


Volume 1, Number 5 


Advertiser Page 

SYNC is published bi-monthly for $10.00 per year 
Blank Cassettes 31 by Creative Computing, 39 E. Hanover Ave., Mor- 
Campbell Systems 23 ris Plains, NJ 07950. Second class postage paid at 
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Computers in Math 47 
Creative Computing Catalog 31 Postmaster: Send address changes to SYNC, P.O. 
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Creative Computing Record 45 
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Lamo Lem 27 
L. J. H. Enterprises 15 Copyright 1981 by Creative Computing. All rights 
MicroAce 25 reserved. Reproduction prohibited in any form. 
New Books > 
New England Software 23 
Softsync 25 
SYNC subscriptions cover 4 The Cover 
Systems and Solutions 21 The cover shows the Sinclair ZX81 computer. 
T-shirts 43 Although available in England since March 1981, 
Worth a Fortune 37 it was formally introduced to the U.S. market on 
Zeta Software 29 October 7, 1981. 


letters 


REM on the 4K ROM 


Dear Editor: 

I have been visiting my brother this 
summer and learning a little about pro- 
gramming the ZX80. Recently I discovered 
something interesting: 

10 REM 

20 PRINT “THIS LINE WILL NOT 
PRINT” 

30 PRINT “THIS ONE WILL” 

In this example line 20 will not print, but 
if line 10 is changed to 

10 REM 1 (or any other character) 

lines 20 and 30 will print. 

We decided that the ZX80 (4K ROM) 
skips the next character after the remark 
command. If that character is a “newline,” 
it skips the entire next line. (Note by his 
brother: The interpreter skips over every- 
thing up to the next NEWLINE, after 
skipping the character following the 
REM.) 

I have really enjoyed your magazine 
and the games that are published. 


David Brendel 
1489 Corn Crib Court 
Stone Mountain, GA 30088 


Dear Editor: 

I would like to warn your readers about 
a semi-bug in Sinclair’s 4K ROM. If you 
use a REM, you must put something after 
it other than spaces. Otherwise, the com- 
puter ignores the next line of the program. 
I have informed Sinclair Research of the 
problem, and I certainly hope they correct 
it in later ROMs. 


Geoffrey Horton 
658 S. Diamond 
Jacksonville, IL 62650 


Ed.— When we received two letters at 
about the same time on the same topic, 
we decided to refer the question to some 
of our sources. Here are their replies: 
David Ornstein—This feature of the 
4K ROM is a powerful debugging tool. 
Suppose you want to check how a partic- 
ular line, say line 150, is functioning in a 
program without going to all the trouble 
of deleting it and then reentering it. You 
simply type in line 149 REM, and RUN 


2 


your program. The ZX80 will run the 
program and skip over line 150. You can 
observe the results and then easily EDIT 
line 149. 

Joseph Sutton—The REM command 
can be used ina line to remove it tempor- 
arily from the program by inserting REM 
immediately after the line number. After 
you have checked the performance, you 
delete the REM. 

James Grosjean— You can use this fea- 
ture as a memory saving tool in some 
programs. For example, in “Motorcycle 
Race” in this issue, you can save six bytes 
by deleting lines 100-114 and substituting 
the following: 


102 GO TO 102+RND(6)*2 
104 PRINT "WATER AND MUD" 


105 REM 
106 PRINT "DEEP HOLE" 
107 REM 
108 PRINT "SHARP TURN" 
109 REM 


110 PRINT '"BUMPY TRACK" 
111 REM 
112 PRINT "FALLEN RIDER" 
113 REM 
114 PRINT "LOOSE GRAVEL" 


“Mini-Billboard” 
for 8K ROM 


Dear Editor: 

When I received my July/August issue 
of SYNC magazine, one of the first pro- 
grams I looked at was “Mini-Billboard.” 
Since I now have the 8K Basic installed 
and I do not want to go back, I looked it 
over to see whether it would be easy to 
convert. 

The only serious problem was finding 
where the character generator was located 
in the 8K ROM. A few weeks before, I 
had obtained a listing of the 8K ROM, so 
I looked for the patterns necessary for 
the character generator. Then all I needed 
was the address. I picked what looked 
like a unique pattern just before the begin- 


ning of the character generator and wrote 
the program: 

10 FOR A=3 TO 9E3 

20 IF PEEK A=0 AND PEEK(A-1)=255 
AND PEEK(A-2)=255 AND PEEK(A-3)= 
201 THEN PRINT A 

30 NEXT A 

(If you are interested in using this, it takes 
almost 5 minutes to run). Now armed 
with the address (7680) I re-wrote lines 
20, 70, and 110 and removed line 21. 

If you change line 10 of the memory 
search program to 17E3 in place of 9E3, 
you will find the pattern occurs twice, at 
7680 and again at 7680 plus 8K (or 8192 
23 = 15872). I would be interested in 
finding out why a particular byte in the 
ZX80 ROM can be addressed at more 
than one place. 

The ‘“Mini-Billboard” program revised 
for the 8K ROM is as follows: 


5 DIM A(8) 
10 INPUT AS 
15 FOR I=1 TO 8 
20 LET A(1I)=(CODE(AS (1) *8) 
+7680 
23 NEXT I 
25 LET F= 
2/ LET L= 
30 FOR X= 
35 FOR I 
40 LET C=PEEK (A(1)+X) 
50 FOR Y=@ TO A 
60 LET E=2**(7-Y) 
70 IF C =E THEN GO TO 100 
80 PRINT "#"; 
90 GO TO 120 
100 LET C=C-E 
110 PRINT "s "; (shift 93 hit 
space) 
120 NEXT Y 
130 NEXT I 
140 NEXT X 
150 LET F=F+4 
160 LET L=L+4 
170 IF L=8 THEN GO TO 30 


My thanks to SYNC for a great magazine 
and to Dennis Duke for a great program. 


Joseph R. Sutton 
170 S. Hillside Ave. 
Succasunna, NJ 07876 


SYNC Magazine 


JRS SOFTWARE 


19 WAYSIDE AVENUE, WORTHING, SUSSEX, BN13 3JU 
TELEPHONE WORTHING 65691 (Evenings and Weekends only) 


ZX80 - PROGRAMMABLE MOVING DISPLAY 

(4K-ROM only) 
Yes! This really is a genuine moving display, not 
another pause routine. If you want moving, flicker 
free displays land who doesn’t] then this is the 
program for you. The secret lies in the ZX80’s ability 
to keep the display on your screen without the need 
to use all of the time available to it. Normally the 
ZX80 would be doing nothing during this spare time 
but the programmable moving display cleverly 
interupts to process your own instructions written in the simple but highly 
effective JRS numeric code. Great care has been taken so that the processing of 
your codes can always be interupted to return to the display routine at the 
precise microsecond that is required to ensure that your T.V. picture remains 
completely rock-steady. 

Normally a true moving display on a ZX80 would take weeks to write and you 
would need to be an expert at machine-code programming. Now, at last, this 
program offers you the ability to write your own true moving displays in under an 
hour with no maching-code experience required whatsoever. 


Cassette with 1k, 2k versions and 3 example programs plus FULL documentation 
£4.95 


Ke 


Example Program 3 


‘ 


i | Shoot the Invaders’ 


ZX81 - SLALOM (16K RAM PACK REQD.) 


e 
Lë Slalom events always draw great crowds to the ski 
A ZZ ZZZ? i | resorts and the T.V. cameras are never far behind. 


Now the skier on your T.V. screen is directly under 
your control and his success in negotiating the 
slalom posts and achieving a fast time relies entirely 
on your skill with the ZX81 keys. 


Cassette and instructions £2.95 


ZX81 - BLACK HOLES (16K RAM PACK REQD.) 


Your starship is in an unknown galaxy consisting 
entirely of black holes which continually threaten to 
swallow you. Your skill at the controls and your 
ability to look and think many moves ahead is the 
only thing that stands between you and destruction. 
How long can you survive! 


Cassette and instructions £2.95 


SPECIAL OFFER SLALOM and BLACK HOLES on one cassette for only £4.50 


OVERSEAS CUSTOMERS Payment must be made in Sterling by International Money Order (available 
PLEASE NOTE at your bank) Please add 50 pence to cover overseas postage. 


“Bar Charts” and 
Rubber Cement 


Dear Editor: 

In my program “Setting Up Bar Charts” 
(SYNC 1:4), additional data can be entered 
in the immediate mode, and the REM on 
line 320 can be eliminated, since J will 
always point to the first element of B 
which contains a zero. Example: LET B(J) 
= 1104. However, the program must be 
run (using GO TO 1) to update the value 
of J each time a value is added to vector 


For those having a problem with putting 
the 8K keyboard template over the old 
keyboard, rubber cement, a temporary 
paper adhesive, seems to do the job. The 
cement remains flexible, and the template 
can easily be removed later if desired. 
The best procedure seems to be to lay a 
thin coat on the keyboard, let it dry a 
couple of minutes, and then attach the 
template. Since rubber cement is highly 
flammable, be sure to take proper precau- 
tions. 


Jon Passler 
344 Cabot St. 
Beverly, MA 01915 


Splitting Strings 


Dear Editor: 

Harry Doakes'’ article on string handling 
in the July/August issue was great. How- 
ever, he didn’t mention one other useful 
technique that rises naturally from his 
explanations—how to split a string into 
sub-strings. The following program will 
do it. 

10 (enter the program shown in SYNC 
1:4, p. 26) 
20 LET A$=“STRING TO BE SPLIT” 
30 LET L$=*” 
40 FOR F=1 TO 13 
50 LET B$=CHR$(CODE(A$)) 
60 LET A$=TLS$(A$) 
70 LET M$=B$ 
80 LET L$=L$ 
90 LET M$=M$ 
100 RANDOMIZE USR(16427) 
110 NEXT F 
120 PRINT L$ 
130 PRINT A$ 

This program has the effect of chipping 

away the leading characters from A$ and 


4 


piling them up, one by one, at the end of 
L$. With the inputs shown above, the 
result will be “STRING TO BE” and 
“SPLIT”. In practice, of course, lines 20 
and 40 will be altered to fit the needs of 
the moment. You can also extend this 
technique to insert a string into the middle 
of an existing string. 


Basil Wentworth 
1413 Elliston Dr. 
Bloomington, IN 47401 


Short Video Cable 


Dear Editor: 

My son, James Willis, got a ZX80 com- 
puter for Christmas 1980, but we have a 
problem. The video cable with the coaxial 
plugs is too short for usage. 

Can we obtain from the manufacturer 
a longer coaxial cable and where specif- 
ically do we do that? 


Charles D. Willis, M.D. 
2490 West Fir Ave. 
Fresno, CA 93711 


Ed. — Check your local electronics supply 
store for a standard coaxial cable with 
standard RCA plugs. If it does not carry 
one long enough for your use, the parts 
should be available to make one. 


The 5-6 Seconds 
of Silence 


Dear Editor: 

When recording programs on cassettes, 
my auto record level cassette machine is 
fooled by the silent period prior to the 
issuance of the message. Due to the silence, 
the gain increases until it is wide open, 
and, when the signal is produced, it initially 
overloads the recording and the results 
are unusable. I have solved this problem 
by not engaging the cassette recorder until 
after 5-6 seconds of silence have passed. 


A. Dan Klyver 
29 Old Stagecoach Rd. 
Weston, CN 06883 


Ed. — See “Perceptions” in this issue for 
more on loading. wv 


Glitchoidz 
heport 


On Hunting Glitchoidz 

A survey of Glitchoid activity reveals 
that they have favorite targets. In addition 
to spaces in PRINT statements noted in 
our last issue (SYNC 1:4, p. 3), semi- 
colons should be carefully observed since 
these help arrange your display. Another 
place to look is in the use of parentheses 
and quotation marks. These must always 
be used in pairs. Another special place is 
in IF statements and the use of the “greater. 
than” and “less than” signs. If there is a 
space in which one might fit, you might 
experiment. 


Handling Character Strings (1:3. p. 6, col. 
1) 
200 LET A=USR(47)-2 


Black Hole (1:3, p. 9) 
52 PRINT, ;I-3;“#”:1-2:“#” 1-1 


Perceptions (1:4) 
p. 6: 
Listing 1. Comments column, 
(4th line: IF HL#DE.. .) 
Dp. 7: 
Listing 2. Hex column, 
Ist line: 217D40 
2nd line: ED5BOC40 
10th line: 48 
Listing 4 
10 REM 217D40ED5BOC4006007CBA 20 
087DBB2004480600C978A E4723 18EE 


Machine Code Keyboard Scanning Pro- 
gram (1:4, p. 8) 

60 IF B> 255... 

100 IF MARK <10 


Screen Scrolling (1:4) 
p. 17, col. 3, add: 
RUBOUT,RUBOUT,ENTER 50 and 
NEWLINE 
RUBOUT,RUBOUT,ENTER 60 and 
NEWLINE 
p. 19, The Great Glitchoid struck an 
almost fatal blow to Dr. Logan’s Road 
Game by chopping the last line of the 
program. 
480 PRINT “*#YOU CRASHED AFTER 
°C; “F#A{MILES#*” 
LIST 40 and SAVE 


Multi-Dimensional Arrays for the ZX80 
(1:4, p. 25) 

240 IFI>9ORI <0... 

270 IFJ> 9ORIJ <0... 


Detective (1:4, p. 36) 
200 PRINT (CHRS$(A(K))): 


Mini-Billboard (1:4, p. 44. col. 1) 
80 PRINT “#”; "a 


SYNC Magazine 


Ke 


SYNC Magazine 


SYNC, a bi-monthly magazine for users and prospective 
users of the Sinclair ZX80 computer has expanded its 
coverage to include the ZX81 as well. 

Now entering its second year, SYNC has been providing 
nearly 10,000 Sinclair computer owners with information 
on how to make most effective use of their computers. 
“Resources,” one of the most popular sections of the 
magazine, has listed over 100 second source vendors of 
software, peripherals and books as well as user groups. 

Each issue of the magazine carries complete application 
programs, tips and techniques for more effective program- 
ming, hardware modifications and in-depth evaluations of 
software, peripherals and books. 

Subscriptions to SYNC cost $10.00 per year (6 issues). 
SYNC, 39 E. Hanover Ave., Morris Plains, NJ 07950. (201) 
540-0445. 


The ZX81 Companion 


The ZX81 Companion by Bob Maunder follows the 
same format as the popular ZX80 Companion. The book 
assists ZX81 users in four application areas: graphics, 
information retrieval, education and games. The book 
includes scores of fully documented listings of short routines 
as well as complete programs. For the serious user, the 
book also includes a disassembled listing of the ZX81 
ROM Monitor. 

MUSE reviewed the book and said, “Bob Maunder’s 
ZX80 Companion was rightly recognized to be one of the 
best books published on progressive use of Sinclair’s first 
micro. This is likely to gain a similar reputation. In its 130 
pages, his attempt to show meaningful uses of the machine 
is brilliantly successful.” 

“The book has four sections with the author exploring 
in turn interactive graphics (gaming), information retrieval, 
educational computing, and the ZX81 monitor. In each 
case the exploration is thoughtfully written, detailed, and 
illustrated with meaningful programs. The educational 
section is the same—Bob Maunder is a teacher—and here 
we find sensible ideas tips, warnings and programs too.” 

Softbound, 5 1/2 x 8”, 132 pages, $8.95. 


The Gateway Guide 


to the ZX81 and ZX80 


The Gateway Guide to the ZX81 and ZX80 by Mark 
Charlton contains more than 70 fully documented and 
explained programs for the ZX81 (or 8K ZX80). The book 
is a “doing book,” rather than a reading one and the 
author encourages the reader to try things out as he goes. 
The book starts at a low level and assumes the ZX80 or 
ZX81 is the reader’s first computer. However by the end, 
the reader will have become quite proficient. 

The majority of programs in the books were written 
deliberately to make them easily convertible from machine 
to machine (ZX81, 4K ZX80 or 1K ZX80) so no matter 
which you have, you'll find many programs which you can 
run right away. 

The book describes each function and statement in 
turn, illustrates it in a demonstration routine or program 
and then combines it with previously discussed material. 

Softbound, 5 1/2 x 8”, 172 pages, $8.95. 


Computers For Kids, 
Sinclair Edition 


Computers For Kids. by Sally Larsen is the fourth book 
in this highly successful series. (Previous editions have 
been released for TRS-80, Apple and Atari computers.) 
Written expressly for youngsters ages 8 to 13, the book 
requires no previous knowledge of algebra, variables or 
computers. Armed with a ZX81 and this book, a child will 
be able to write programs in less than an hour. A section is 
included for parents and teachers. 

The book starts with a patient explanation of how to use 
the Sinclair, graduates to flow charts, and simple print 
programs. The twelve easy-to-read chapters go through 
loops, graphics and show other programming concepts, 
and show in a painless way how to make the computer do 
what you want. 

Donald T. Piele, Professor of Mathematics at the University 
of Wisconsin-Parkside says, “Computers For Kids is the 
best material available for introducing students to their 
new computer. It is a perfect tool for teachers who are 
learning about computers and programming with their 
students. Highly recommended.” 

Softbound, 8 1/2 x 11”, 56 pages, $3.95. 


Order Today 


To order any of these books, send payment plus $2.00 
shipping and handling per order to Creative Computing 
Press at the address below. Visa, MasterCard and American 
Express orders should include card number and expiration 
date. Charge card orders may be called in toll-free to the 
number below. 


creative GCorpatirg 


Toll-free 800-631-8112 
In NJ 201-540-0445 


39 E. Hanover Avenue 
Morris Plains, NJ 07950 


Sync MOLES ees 


Paul Grosjean 


SYNC Program Listings 

Readers should note the following con- 
ventions used in the program listings in 
this issue: 

# ore = Used in PRINT statements to 
show necessary spaces. 

“A” (shift) = Used in PRINT statements 
to indicate graphics; in this case use the 
graphic on shift A. 

INPUT = Used in PRINT statements 
to show that the keyboard key or token 
should be used instead of spelling out the 
word (Richard McDaniel’s article in this 
issue). 

In some schematics you may have 
noticed a designation given as 2K2. This 
is U.K. usage. U.S. usage is 2.2K. SYNC 
follows U.S. usage, but occasionally a U.K. 
schematic does not get completely con- 
verted. 


8K ROM Problems 

Several readers have asked for infor- 
mation about 8K ROM problems they 
had encountered. We referred the question 
to Sinclair, USA, and this is Nigel Searle’s 
answer: “Some 8K ROMs have a bug. We 
are waiting for a new batch of correct 
ROMs from our supplier. This may take 
several weeks. In the meantime, please 
write your name, address, and the words, 
“8K ROM” on a piece of paper and send 
it to Sinclair Research, 50 Staniford St., 
Boston, MA 02114. We will then send 
you a new ROM as soon as they are 
available. We apologize for any incon- 
venience you may have been caused.” 

How do you know whether your ROM 
is one with the bug? The bug seems to 
show up only in certain arithmetic com- 
putations using large numbers. David 
Orstein has supplied us with a simple test: 
Try having your 8K ZX80 print 22. The 
answer shown should be 4,294,967,300 
(actually 4,294,967,296). Then print 2°2-1. 
If the answer given is anything other than 
the first answer minus 1, you have one of 
the ROMs with the bug and you should 
send in as above. However, Nigel Searle 
has emphasized that you should keep your 
present 8K ROM until it is replaced and 
that it should cause no problems in normal 
programming. 


6 


SYNC Subscriptions 

SYNC subscribers have now passed 
the 8000 mark. Up to this point all sub- 
scriptions have begun with the first issue, 
but now we have to start with the second 
issue. 


ZX Microfair 

The first show centered on the ZX80/1 
computer will be held on September 26, 
1981, at Central Hall, Westminster, London. 
Mike Johnson is organizing the show in 
association with the National ZX80/1 Users 
Club. Hardware and software suppliers 
will have space for their wares. “We hope,” 
says Mike, “that the exhibition will prove 
an excellent market-place for the exchange 
of ideas and information, as well as giving 
people a chance to display and sell pro- 
grams and peripherals.” 


SYNC in Microcomputer Index 

SYNC is now one of the twenty micro- 
computer magazines included in Micro- 
computer Index, a recent entry into 
periodical indexing. 

Since the field of microcomputers is 
growing so rapidly, one of our big problems 
is finding out what others are doing. One 
answer, of course, is to subscribe to every 
magazine that might cover the topics we 
are interested in. Microcomputer Index 
provides an alternative and promises to 
be a major resource for those people 
working (and/or playing) in the field. Users 
will be able to keep up with what is going 
on and to pinpoint the articles that will be 
of most use. 

The Index has two sections. In the first 
section articles are indexed alphabetically 
by title under nearly 300 topic headings 
which are listed together in the front of 
the Index. The title is followed by the 
author’s name, an abstract number, a 
classification by type (article, book review, 
column, hardware review, letter, software 
review), the language of the program listing, 
the magazine, the volume and issue 
numbers, and the date of issue. 

In the second section the same infor- 
mation is given under the magazine name 
for each issue covered by the current 
index. Entries are made in the order of 


appearance in the magazine. In addition, 
an abstract of the article is given along 
with the list of topics under which it is 
indexed. These abstracts are brief, usually 
about 25 words, and on target (at least as 
far as the SYNC articles surveyed are 
concerned). 

The current issue runs 96 pages and 
includes about 1250 articles. The Index, 
now into its second volume, is published 
by Microcomputer Information Services 
(see SYNC 1:4, Resources, p. 48). 


SYNC NOTES: UK 


Sinclair Launches the ZX Printer 

Sinclair Research has introduced the 
long awaited ZX Printer for the ZX81 
and ZX80 (8K ROM only) at the PCW 
show in London in early September. The 
printer is available only from Sinclair by 
mail order at £49.95 inc VAT. 

ZX80/1 users will now be able to get 
hard copy of their listings. The printer 
features full alphanumerics and sophisti- 
cated high resolution graphics. The special 
features include COPY, which prints out 
exactly what is on the screen without 
further instructions. The operation is com- 
plete in 14 seconds at an effective cost of 
less than 1p. L LIST instructs the printer 
to produce an entire completed program, 
and L PRINT to print copy out on the 
printer and not the screen. The copy has 
32 characters to the line, 9 lines to the 
vertical inch, and a printing speed of 50 
characters per second. It is attached to 
the rear of the computer by a stackable 
connector which allows the 16K RAM 
pack to be used at the same time. The 
special aluminized paper comes in 65- 
foot rolls which will take care of over 250 
full screens of text. The paper will be 
supplied in packs of five for £11.95. 


Sinclair to Sell ZX81 Retail 

Sinclair has signed an exclusive trial 
agreement to sell the ZX81 retail through 
over 100 W H Smith high-street stores. 
“Both parties view the agreement as an 
experiment,” commented Clive Sinclair, 
Chairman of Sinclair Research. Under the 
initial five month agreement Smith’s will 
set up new computer departments in each 
store with specially trained staff to demon- 
strate the ZX81 and give after-sales service. 
Sinclair products will sell at the normal 
prices, but the new ZX Printer and ZX81 
kit will not be available for the time 
being. 


SYNC Magazine 


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September/October 


Currently Technical Services Manager, 
David Ornstein has been with Sinclair since the 
opening of its U.S. office. He has been involved with 
Sinclair's technical hotline, technical writing, and 
machine servicing. His primary interests are in 
the areas of software and hardware R & D, and 
system integration. 

His secondary interests are reading (Frank Herbert), 
listening (Pink Floyd) and sharing 


Bercentions 


Ld a D 
David Ornstein 
ae 
Listing 1. 
Label Assembly Comment 
; Copyright (c) 1981, 
by Sinclair Research Ltd. 
SAVE: ; SAVE RAM 
! ; 
A ROM Munching ; Address=0186 hex 
a 0438 decimal 
Session 
; Save from 4000h to (E.LINE) 
H 
FOP DE 3; remove return address 
, LD DE, 4811 Lead in 
Overview LSAV2: LD A,7Fh ; KB mask 
One important aspect of a computer is IN A, (OFER) ; paiga aap Ka zero and 
e ; rea ey 
its I/O (Input/Output) system. The I/O i gayo; RRA ; move BREAK into CY (carry) 
functions provided by a given computer JR NC,LSS ; if BREAK pressed 
system govern the usefulness of that system. DINZ $ ; Wait 255*13+65 T-States 
The ZX80 is slightly limited by its storage J eee me) eath time around 
. 3 the LSAV2 silence loop; 
system. With a ZX80, you can SAVE a ; i.e., 5 seconds in all 
program and LOAD it back in again. DEC DE 
Granted, your variables are SAVEd (and LD A,D 
LOADed) with your d a 
W ; you program, SO you OO JR NZ,LSAV2 3 if DEO | 
have some limited data storage. But, LD HL,4000h ; now dump RAM | 
imagine a program which takes an inde- LSAV27: LD DE, 8+(248,sh1.8) 5 i T » e=8, d=248 
. LSAVZ: RLC (HL) ; get next bit 
pendent set of data (e.g., a text file), SBC A,A s, FF if ai, 00 if 0 
operates on it (e.g., a text editor or com- AND 5 ; Sif a 1,0 if o 
piler), and produces some arbitrary output ADD A,4 : 
: : LD C,A 3; cs=*9 if al, 4if a O 
(e.g, a machine code program), This PP LSAV4 OUT (OFFh),A ; tone burst 
of program is sometimes known as a filter. ID B,36 ; DELAY 
The difficulty is that you have no way of DINZ $ ; LOOP 
etting the independent data to the pro- EP Berk 
a P EES IN A, ‘(OFFEh) 5; set output to zero 
‘ ; ; ; and read BREAK key 
One solution to this problem is to have LD B,35 ; DELAY 
a copy of the filter (program) for each set SE o p Loor 
of data. This is not a very efficient method, JR së LSav4 
D D e e 3 3 
but it does have the advantage of simplicity. LD B,D ; get timing for IB gap 
However, I believe that a user should LSAVS: NOP 3 inter-bit gap 
have a choice between filter copying and Tr SS 
. ¥ 
independent data storage. Then he can DEC E 
make his own trade-off decisions, thus JR NZ. LSAV3 ; if more bits 
utilizing the better method for his appli- Gidd , b 
. JR NC, LS8 ; if BREAK pressed 
cation. — l l CALL ENDBYT e 
In this issue, I will take you on a journey JR LSAV27 
through the ZX80’s storage system. I will ` ENDBYT: ae eae EE ane 
show you how to utilize the LOAD and á DAVE at and of byta wei 
e e 5 3 s 
SAVE routines in the ZX80’s ROM (Read. ; 72 T-States including call 
Only Memory), and apply them wherever, 3 and return if returns. 
and however, you want. But first I will bh mm. f Soap porote 
run through, in detail, the algorithm(s) LD HL, (E-LINE) 
used by the ZX80’s cassette system. For SCF ; carry = 1 
the greatest level of understanding you ange PZ = DE > ferry 
D D D s 
should follow the code in Listing 1 very RET NC ; unless end of area to be dumped 
carefully. POP HL * discard return addr from ENDBYT 


8 


SYNC Magazine 


LL is 


LL23 


LL27: 


LLZ: 


LA 


LESE 


LLó: 


LLZ: 


Assembly 
JR NEWLIN 


POP DE 
LD DE, 22290 
LD 9,7Fh 

IN A, (OFEh) 
RLA 


JR NC, LSB 
RLA 
JR C,LL1 


JR NZ, LL2 

INC (IY+E-LINE+1— 
4000h) 

LD HL, 4000h 

LD E, 8 

LD A, 7F 

IN A, (OFEh) 

RRA 

JR NC, LL7 

RLA 

RLA 

JR NC, LLZ 


L be, 148 
LD B, 26 


DEC C 
IN A, (OFEh) 


RLA 
BIT 7,C 
LD A,C 

JR C, LL4 
DJNZ LLS 


JR NZ, LLë 
CP 86 
JR NC, LLZ 


CCF 


RL (HL) 
DEC E 

JR NZ, LLZ 
CALL ENDBYT 
JR LL27 


DEC D 

JP P-O 

DEC (I Y+E - LINE 
+1 — 4000h) 


Comment 


LOAD RAM 


wr 


3 Address = 206 hex 
318 decimal 
LOAD from 4000h on 


a 


first look for lead-in: read 
every 15.1 ps if 1°s, 21.5 ws 
if OS, wait until get 

zeroes for 480 ms, abort to 
NEWLIN IF BREAK pressed 

CY = cassette data 

if high then no leader yet; 
SO go back 


we 8 wes s «2s “8 88 WE 


3; if DE#0 
in case is 40h now 


get cassette/BREAK data 
put it in CY (BREAK, that is) 
if BREAK 


sa we op 


CY = cassette data 
read every 16 ais until ail is 
found 


we ‘88 was 


req'd 408 ais trailer after 

tone burst 

count 15.4 us if ai, 15.2 if ao 
N.B. C is decremented at least 

26 times, i.e., to 122 which 

has bit 7=0 


“eae s «wes SS ws We 


test bit 7 


until end of trailer then 
exit with carry clear 
if>+X2.3 ms, is a 1 


ws WE wee 98 ag 


if <%0.8 ms, is noise 


; here if data bit: carry set 
3 if O, clear if 1 
3 shift bit into dest 


S go get next bit 
; here after 8 bits 


3 if have been through ENDBYT 
3 else restore E-LINE 


JR LS8 
eee 


September/October 


Save 

The first thing the SAVE routine does 
is to POP a value off the stack. This is the 
address of the instruction after the CALL 
to SAVE. Since SAVE does not ever return 
there (it either goes to NEWLIN [the 
section of the ROM that gets a new line 
of Basic] or to NEW), it does not want to 
leave the stack cluttered with its RETurn 
address. 

By listening to a SAVEd program on 
tape, you will notice that the first element 
of a SAVEd program is a 5 second silence. 
This is generated by the next section of 
code. The DE register pair is loaded with 
4811 (decimal), the number of times to 


execute the “silence loop.” 
The silence loop runs for 1.04 micro- 


seconds (millionths of a second) each time 
around, and its algorithm is as follows: 
First, load the keyboard mask to read the 
BREAK key. (See SYNC 1:3, “The ZX80 
Keyboard,” for details on the ZX80's key- 
board system.) Next, read the keyboard/ 
cassette input port. This has the effect of 
resetting, to zero, the output to the cassette 
port. The RRA instruction, at LSAVO is 
used to rotate bit 0 of the input register, 
A, into the carry flag. This bit represents 
the BREAK key data. Then, if NC (No 
Carry) is true, the routine jumps to LS8, 
the abort section of the code, because 
BREAK was pressed. The DJNZ instruction 
is used to create a delay. Finally, the loop 
counter, DE, is decremented and compared 
with 0. If it is zero, then SAVE has executed 
the loop 4811 times (i.e. 4 , 5 seconds). 
Otherwise, the computer will proceed back, 
to LSAV2, and execute the loop again. 

Now we are ready to SAVE RAM 
(Random-Accesss Memory). Here things 
Start to get a bit hairy. The next section 
of code begins by picking up the start 
address for the SAVE, 4000h, and putting 
it in the HL register pair, the address 
pointer. The character loop begins here. 
It starts by setting D=8 (i.e., the number 
of bits in a byte). Now, set E=248 (De, 
the loop constant for the inter-bit gap 
[see later]). 

The bit-save loop starts next (LSAV3). 
It proceeds as follows: First, execute an 
RLC (HL) instruction. This rotates the 
memory location pointed to by HL, left 
via the carry flag (i.e., everything shifts 
left one bit; bit 7 moves into the carry 
flag; bit 7 moves into bit 0). This operation 
is depicted in Figure 1. 


"ailes 


<— (HL) 


Figure 1. The RLC (HL) instruction. 


ee eee 


Notice that the bit-save loop executes 8 
times, so the computer cycles through all 
the bits of the source once, and returns 
the location pointed to by HL to its original 
value when done with that byte. Next, 
execute an SBC A,A (SuBtract with Carry) 
instruction. In a nutshell, this instruction 
says: set A=A-A-carry; i.e., A=-1 if the 
bit, held in carry, is a 1, and A=0 if the 
bit is a 0. (NR -1d =FFh. Also -1d =1111 
1111b.) So now we have A=0000 0000b if 
the bit we are SAVEing is a 0, otherwise 
A=1111 1111b. Execute an AND 5 instruc- 
tion. This sets A equal to 0 or 5. Now, 
ADD AA (add 4 to A). Finally copy A 
into C with an LD C,A instruction. 

At this point C=9, if we are SAVEing a 
1 bit, and C=4 if we are SAVEing a 0 bit. 
This number is the loop constant for the 
“tone loop.” Basically, the tone loop’s 
algorithm is: 


1) Set cassette output=on (Create a 
tone). 

2) Delay. 

3) Set cassette output=off. Read the 
BREAK key. 

4) Delay. 

5) Decrement C (the number of times 
to execute the tone loop). 

6) If C#0 then go back to step 1. 


For a full understanding of how the hard- 
ware generates a tone, a detailed study of 
the ZX80’s schematic diagram is required. 
That is, however, beyond the scope of 
this article. 

We continue the bit-save loop, by loading 
B with E (the inter-bit gap loop constant), 
and performing NOP (NO oPeration) 
instructions. (The DJNZ instruction is a 
special Z80 looping instruction. It says: 
decrement B and JR (Jump Relative) to 
some arbitrary memory location (LSAVS, 
in this case) if B#0.) Finally, decrement 
D, the number of bits in this byte, to 
SAVE and jump back to LAV3 if D#0. 

If you look back and review the tone 
loop, you will notice that step three not 
only resets the cassette output, but also 
reads the BREAK key. This leaves bit 0 
of A=0 if BREAK was pressed. The next 
two instructions, RRA (Rotate Right 
Accumulator) and JR NC,LS8, move bit 0 
of the accumulator into the carry flag, 
and jump to LS8 if NC (i.e., BREAK was 
pressed). 

SAVE nears completion by CALLing 
the subroutine ENDBYT, which increments 
HL, the pointer to the byte to SAVE, 
and, if there is more memory to SAVE, 
i.e., HL <(E-LINE), it returns. If ENDBYT 
finds there is no more memory to SAVE, 
it jumps to NEWLIN, which is the main 
section of the 4K Basic. If ENDBYT 
RETurns to SAVE, the instruction after 
the CALL ENDBYT, a JR LSAV27, causes 


10 


the computer to go back and SAVE 
another byte. 


Load 

LOAD also begins with a POP operation, 
used to remove its return address from 
the stack, thus insuring clean operation. 
At LL1, DE is loaded with 22290d. This is 
the loop constant for the leader loop. 
The leader loop proceeds as follows: 


1) Read the keyboard/cassette port. 

2) If BREAK is pressed, jump to LS8. 

3) If cassette port = one then go back 
to step 1. 

4) Decrement DE (the loop constant). 

5) If de#0 (i.e., not 5 secs. of silence 
yet) then go back to step 1. 


In essence, this loop searches for about 
5 seconds of silence on tape. If a one is 
found during this time, it goes back and 
resets DE, the loop counter, thus reinitiating 
the 5 second search. 

If BREAK is presed during this period, 
the LOAD routine jumps to LS8, which, 
in turn, jumps to NEWLIN. This allows 
you to change your mind about LOADing 
a program without deleting the program 
currently in memory. Hitting BREAK after 
the first byte has been transferred from 
cassette into RAM, however, is a destruct- 


ive action. 
Now we are almost ready to start LOAD- 


ing into RAM. The final pre-LOAD step 
is to increment the high byte of E-LINE. 
This is done, in case this byte is 40h, to 
assure that ENDBYT permits at least 256 
bytes to be loaded. Once this first page 
(256 bytes) of memory is LOADed, E- 
LINE, a system variable which resides in 
the first page of RAM, will have been 
overwritten with the appropriate value. 

The routine at LL7, which is where 
LOAD jumps if BREAK is pressed after 
the silence loop finishes, tests to see if 
LOAD has been through ENDBYT, i.e., 
at least one byte has been LOADed. If it 
finds that LOAD has not called ENDBYT 
yet, then it permits the BREAK to be 
non-destructive. After decrementing the 
MS (Most Significant) byte of E-LINE 
back to its original value, it jumps to LS8, 
and thus back to NEWLIN. If ENDBYT 
has been called, the LS8 routine jumps to 
location 0, effectively resetting the com- 
puter. 

Finally, we can begin to LOAD data 
into RAM. LOAD continues by loading 
HL, the destination byte-pointer, with 4000h 
(16384d) (i.e., the address of the first RAM 


location). Next, E is set to 8: the number 
of bits in a byte. The character loop begins 
with this instruction (LL27). The bit loop 
begins next (LL3). 

The first four instructions of the bit 
loop are used to read the cassette/keyboard 
port and, if BREAK is pressed, jump to 
LL7. Next, two RLA (Rotate Left Accum- 
ulator) instructions are executed to rotate 
the cassette data into the carry flag. If the 
carry flag is clear (i.e., the cassette port 
was at logic 0), then LOAD jumps back to 
LL3. This section of code, by reading the 
cassette port every 16 microseconds, waits 
until 1 is found. This 1, which represents 
a tone burst, marks the beginning of a bit 
frame. 

As soon as 1 is found, the loop falls 
through, and C is set to 148d. C is used to 
count the sum of the durations of each 
pulse and their trailers found during this 
bit frame. When the bit loop finally falls 
through, after the LL5 instruction, the C 
register is checked to see how long the 
input was on. If bit 7 of C is reset (e, 
C>#22.3 ms), the JRNZ,LL6 instruction 
jumps to the routine at LL6 which shifts 
the bit into the destination. Otherwise, if 
C < 86 (i.e., C<% .8 ms) the input was 
noise, so go back to LL3 and continue 
looking for the next bit. If the JR NZ, LL3 
instruction (used to test for noise) falls 
through, the LL6 routine executes. 

In LL6 an RL(HL) instruction is used to 
rotate the bit found on the cassette port 
into the destination. This is followed by a 
DEC E instruction and a JR NZ,LL3. This 
pair is used to go back and get the remain- 
ing bits for this byte. When E=0, the 
current byte has been filled, the bit loop 
falls through, and ENDBYT is called. If 
ENDBYT comes back, a JR LL27 is exe- 
cuted and the computer goes back for 
the next byte. 

Reviewing the LOAD and SAVE rou- 
tines, you will notice in each, an LD 
HL,4000 instruction. This instruction loads 
HL, the byte pointer, with 16384d (4000h), 
the address of the first memory location 
to SAVE or LOAD. Also, looking at 
ENDBYT will reveal that the system vari- 
able E-LINE holds the address of the last- 
byte-to-SAVE (or LOAD) plus 1. These 
two values, the 4000h in the LD instruction, 
and the contents of E-LINE, can be modi- 
fied to allow any area of memory to be 


SYNC Magazine 


SAVEd or LOADed. My modification to 
these routines, to make the SAVE/LOAD 
area fully programmable, is to change the 
LD HL,4000h to an LD HL,x, where x is 
the address of the first memory location 
to SAVE from or LOAD to. Then, each 
time before you use the routines, POKE 
the appropriate value into E-LINE. The 
second part is easy. The first, however, is 
impossible (or almost). The difficulty lies 
in the fact that the LOAD/SAVE routines, 
and therefore, the LD HL,4000h instruc- 
tions they contain, are in ROM. And you 
cannot change a ROM! 

There is, however, a solution: copy the 
routines into RAM. Then, when you want 
to use the routines to SAVE/LOAD some 
section of memory, just POKE the start 
address into the two byte address field of 
the LD HL,xxxx insstruction. Next, POKE 
the address of the first byte not to SAVE/ 
LOAD Ge, the last-byte-address + 1) 
into E-LINE. Then, instead of using*the 
LOAD or SAVE commands from Basic, 
use a USR(x) call to execute your modi- 
fied versions of cassette handling routines 
in RAM. 

This method of utilizing the 4K ROM’s 
SAVE and LOAD routines has many pos- 
sible applications. You can SAVE and 
LOAD not only independent programs 
and data, but any area of memory. This 
means, for example, that you could write 
a program to selectively SAVE/LOAD 
some arbitrary (group of) variable(s). You 
could write a subroutine, for your text- 
editing system, that SAVEd a string array 
(i.e., a list of lines of text). You could 
then write a corresponding LOADer routine 
for your PASCAL compiler, which 
retrieved the text from tape. You could 
write a machine language monitor/ 
debugger/editor (MDE) which allowed you 
to SAVE/LOAD machine language pro- 
grams in any format you desire. 

This capability of independent data 
storage has been missing from the ZX80’s 
repertoire for too long. I hope this article 
will give you the basics required to apply 
this powerful technique. If the reader 
response is great enough, some particular 


September/October 


Modulator 


i Not shown on schematic. 
Included in USA 
Ch. 2 machines only. 


(Not Included) 


Shown on schematic. 
Excluded in USA Ch. 2 machines only. 


Figure 2. 
The above correction applies to USA machines running on channel 2. 
It does not apply to channel 36 ZX80 kits. The transistor is used, in place 
of R32, to pull the composite video signal, running into the video modulator, 


low during sync time. 


applications could be developed in a future 
column. Something I am working on, also 
perhaps for a future column, is a full 
fledged I/O processing system. It could 
handle reading and writing of records 
(blocks of data) in a cassette system. With 
a little bit of electronics, it could even 
control the motors in your tape recorder. 


Video Sync Signals 


Some owners have told me that they 
have tried my direct video circuit to drive 
a monitor (see ZX80 Technical Manual/ 
SYNC 1:2, p. 12), apparently to no avail. 
The problem seems to be that some moni- 
tors require external sync sources. Vertical 
sync can be obtained from IC11/pin22 
(for negative-going signals) and IC11/pin10 
(for positive-going signals). Horizontal sync 
can be tapped from IC19/pin6 and IC19/ 
pin5 for positive-going and negative-going 
pulses, respectively. These signals must 
usually be provided to separate terminals. 
Some monitors provide internal syncing 
as a selectable option. If yours does, use 
It. 


Video Modulator Drive 
Circuitry 


If you have a standard U.S. version 
ZX80, running on channel 2 (VHF), then 
your computer includes some extra cir- 
cuitry for driving the video modulator. 
This information is not supplied with the 
ZX80 schematic. The circuit is shown in 
Figure 2. 

The circuitry is used to superimpose 
negative-going sync pulses onto the video 
signal. Your schematic probably shows 
R2 used for this purpose. However, it is 
done this way only in the U.K. (channel 
36, UHF) machines. R32 is not included 
in U.S. Channel 2 machines. 


Loading 


As you probably know, if not from 
experience, then by reading about it, the 
LOADing problem has been one of the 
greatest difficulties associated with ZX80s. 
In my dealings with machines, however, I 
have found that most of the units returned 
with a claim of “I CAN’T GET IT TO 
LOAD!!!!” work fine. Therefore, the 
assumption I must make is that the pro- 
cedures being followed are incorrect, or, 
not being followed correctly. I will detail 
everything that Sinclair and I, as an indi- 
vidual, have learned about LOAD prob- 
lems. The following six items are relevant 
to the situation. 

1) Try cleaning and demagnetizing the 
record/playback heads of the tape record- 
er. Your ear may not pick up the signal 
fluctuations due to magnetic flux on the 
tape heads. The ZX80, however, has a 
much more sensitive “ear.” 

2) Use a good quality tape. A “DATA 
TAPE” works well. 

3) Check the output level of your tape 
deck’s EAR/SPKR jack. It must be at 
least 4 volts peak-to-peak (5 to 6v p-p is 
best). If you do not have a signal with 
enough amplitude, the ZX80 will continue 
looking for your program forever, and 
the TV screen will remain indeterminently 
gray indefinitely. 

4) Do not use the output from a hi-fi 
amplifier, as this may damage your com- 
puter. 

5) Try loading with only the EAR jack 
connected. 

6) A DIN-type socket usually gives only 
about 1.5 volts peak-to-peak (or less). 
Therefore, it is unsuitable for use with 
your ZX80, unless equipped with an exter- 
nal buffer circuit. 

Well, that’s it for this issue. Until next 
time. Same relativistic time period. Same 
non-Euclidian universe. 


11 


8K ROM 
16K RAM 


12 


GRA+PIX: A System for Pixel Graphics 


The following article describes a set of subroutines for 
drawing lines, arcs, regular geometric shapes, and sectors on 
the Sinclair ZX80 with the 8K Basic ROM and 16K RAM. 
The routines should also work on a ZX81 with 16K RAM. In 
addition, in SLOW mode on the ZX81, you can watch the 
figures develop as they are drawn, although for some shapes, 
such as “filled” circles, this will be a very slow process as 
many points must be calculated before they can be plotted on 
the display. 

The routines presented are useful for displaying data 
pictorially as pie charts, histograms, and line charts. They are 
not suitable for animation, so no attempt has been made to 
optimize them for speed. Also it is left to the reader to 
provide labeling and titling routines. This is a chore that is 
best tailored to the individual application, and it should not 
be difficult to do. 

The routines require a full D-FILE to be effective, thus 
smaller memory systems could not use the package as is. 
Those users with 8K of RAM (see SYNTAX ZX80, March 
1981) should be able to use the entire package. Those with 
4K of RAM will have to delete the driver (lines 1 through 255) 
and the fill routine (lines 9750 through 9895) to fit memory 
and supply the required parameters by assigning the variables 
directly before calling the GRA+PIX subroutines. You will 
have to experiment to see how useful this is. 

The term graphic means literally to form by writing, drawing, 
or engraving —a product of graphic art. Graphics is the art of 
representing an object on a two-dimensional surface by means 
of some mathematical rules of projection. 

The least rigorous interpretation of a graphic representation 
is then as simple as a list of words or numbers on a piece of 
paper set there to convey some meaning to the intended 
audience. Thus all computer programming languages have 
some degree of graphic capability. They are all capable of 
displaying information, either on a hardcopy device, such as 
a printer or terminal, on a display surface, such as a CRT, or 
in some other fashion so that the recipient of the information 
is able to understand what the computer and the program did 
for him. 


Robert B. Keller, 1004 Skyline Drive, Rochester, MN 55901. 


Robert B. Keller 


With the advent of Basic and the various time-sharing and 
microcomputer Basic implementations, computer capability 
has been put within reach of large numbers of people. As 
these people have become familiar with using the computer, 
they have demanded and received enhancements in the 
language. One significant area is the graphic capability of the 
Basic language. Text graphics is no longer sufficient. With 
the ability to create moving displays and the capability to 
form characters by merely setting an electron beam on or off, 
it became desirable to create picture graphics. 

The various microcomputers offer similar ways to do this. 
With commands such as SET, PLOT, and DRAW,, the user is 
given the ability to turn on or off picture elements (pixels) on 
his video display in any order by specifying some coordinate 
point, x-y, and stating whether the point is to be turned on or 
turned off. Once could laboriously construct any image he 
wished (within the resolution of the screen) by turning on all 
the pixels he needed to make the desired image. 

However, this can be quite tedious and the novelty of using 
graphics would quickly vanish if there were not a better way. 
Fortunately, there is an easier method for many applications 
of picture graphics. Consider drawing a straight line from the 
point x=10, y=10 to the point x=50, y=50. One way to do 
this would be the following simple program. 

10 LET Y=10 

20 FOR X=10 TO 50 

30 PLOT X,Y 

40 NEXT X 
The result of this program is a straight line from (10,10) TO 
(50,10). We could change the vertical displacement of the 
line by changing line 10: 

10 LET Y=20 
and we would now have a straight line from (10,20) to (50,20). 
We could even ask for the value of y to be input: 

10 PRINT “INPUT Y” 

11 INPUT Y 
and we could draw horizontal lines all over the screen. So far 
not very exciting, but it gets better. In a similar fashion we 
could give a single value of x, allowing y to vary and PLOT 
vertical straight lines. But how about lines at any angle, from 
any point (X0,Y0) to any other point (X1,Y1)? 

Let us throw away the simple straight line program and 
brush up a bit on our high school geometry. Look at your 
Basic manual in the section describing PLOT and UNPLOT. 


SYNC Magazine 


Note how the screen is divided for these commands. The 
screen consists of small cells, or pixels, in the horizontal (x) 
and vertical (y) directions, counting from x=0 to x=63 and 
y—0 to y=43, with the origin at (0,0) in the lower left-hand 
corner of the screen. This looks just like the graph paper we 
used to use in high school. 

Remember quadrants? If we look at the graph paper, or 
screen in this case, and if we take a point in the center, say 
(x=30,y=20), and draw a vertical and horizontal axis line 
through that point, we would have the screen divided up into 
four sections, or quadrants. The upper right quadrant is 
quadrant I, the upper left quadrant II, the lower left quadrant 
III, and the lower right quadrant IV. See Figure 1. 


Quadrant II 


Quadrant I 


Quadrant II Quadrant IV 


Figure 1. 


Now if we draw a straight line from the origin of this graph 
paper, (30,20), to another x-y point, (50,20) we have a horizontal 
line lying on the x-axis of the first quadrant. Suppose we draw 
the line from (30,20) to (30,40). We have a straight vertical 
line lying on the y-axis between the first and second quadrant, 
at 90 degrees (one quarter of a circle) to the first line. Now 
draw a line from (30,20) to (50,40). This is still a straight line, 
but now it lies half way between and x and y axes, at a 45 
degree angle. Without getting too rigorous (or boring) in our 
mathematics, we can develop a relationship between the line 
we want to draw and the x and y coordinate points using a 
little geometry. 

Draw a triangle with the base a straight line from (30,20) to 
(50, 20). Draw a vertical line from (50,20) to (50,40). Now 
connect the top of the vertical line (50,40) to the origin 
(30,20), and we have our triangle. The diagonal line is the one 
we want to express geometrically. See Figure 2. 


Figure 2. 


September/October 


Between the lines (30,20) to (50,20) and (30,20) to (50,40) is 
an included angle. Let us call it angle A. We can solve for the 
value of this angle (forget that we already know it is a 45 
degrees or PI/4 radians) by using the relations: 


SIN A Opposite side / Hypotenuse 
(40-20)/SQR((40-20)**2 + (50-30)**2) 


20/SQR(800) = 0.707106... 


The angle whose SIN (ASN) is 0.707106..... is 45 degress or 
PI/4, which we already knew (in this case). The equation for 
SIN A can be generalized: 


SIN A = (Y1-Y0)/SQR((Y 1-Y0)**2+ (X1-X0)**2) 
A = ASN((Y1-Y0)/SQR((Y 1-Y0)**2 + (X1-X0)**2)) 


Now that we have A, so what? Well, for one thing we can 
now solve for the line we want to draw from (30,20) to (50,40) 
in this case, or better, from (X0,Y0) to (X1,Y1) in general. 
Using geometry the line we want (the hypotenuse of our 
triangle) is related to the tangent of the angle A we just 
calculated. The tangent is merely the ratio of the SIN to the 
COS, TAN A = SIN A/COS A, and can be used in the 
following manner. 

For values of x from X0 to X1, in steps of 1, the value of y is 
calculated as: 


DY = SGN (Y1-Y0)*TAN A 
Ycurrent = Yprevious + DY 


Thus, treating x as the independent variable we are able to 
calculate the value of each point along the desired line 
geometrically. Listing 1 is a routine for drawing a straight line 
from any point (X0,YO) to (X1,Y1). The routine takes into 
account that you may have division by zero possibilities 
(drawing a point) and optimizes the line for the fit. The 
quadrant is taken into account. The missing lines will be 
supplied later. The variable P is the PLOT/UNPLOT control. 
If P=0, the routine will UNPLOT. 

For each routine the SYNCSUM is supplied so you can 
check your entry as you go (see SYNC 1:4, pp. 6-7). Begin by 
entering the LINE routine in a NEW workspace. Enter the 
lines as they are listed, making the line deletions when asked 
to do so. Each SYNCSUM is obtained by examining the 
contents of memory at the time, so if you want to check your 
SYNCSUM with that on the listing, it is important that lines 
be entered in sequence. Also, do not use tokens in REM 
statements to save space but spell words out exactly as listed 
so the correct SYNCSUM is obtained. 


er eu SORT 


ALGORITHM 
| To UR NA MENT 
TODAY 

A4. og d 


13 


9000 REM LINE (XO9YOeX1leV1loeP) 
9015 IF XO<>KL GR YO<>YL THEN GÜ 
TO 9040 

9020 LET S=2 

9025 LET DX=9 

9030 LET DY=0 

9035 GOTO 9105 

9040 REM CHECK SLOPE OF LINE 
9045 LET A=ABS ((Y1-YO)/SQR2 ((Y1 
-~YO)*(Y1-YU) + (X1-X0) *(X1-X0))) 
9050 LET A=ASN (At(1-A)*®(A>L)) 
9055 IF A>PI/4 THEN GOTO 9085 
9060 LET D=2%(ABS (X1-X90) +41) 
9055 LET DX=SGN (X1-X0) 

9070 LET Dresch (YL-YO)=TAN A 
9075 IF ABS OY<1E-7 THEN LET Dy: 
O 

9080 GOTO 91905 

9065 LET D=2*(ABS (YL-YO)+1L) 
9090 LET DX=SGN (X1-X0)*#COS A/SSI 
N A 

9095 IF ABS OX<1LE-7 THEN LET DX= 
0 

9100 LET DY=SGN (Y1-YO) 

9105 LET X2=X0-DX ` 

9110 LET Y2=YO-DY 

9120 FOR I=1 TO D/2 

9125 LET X2=X2+DX 

9130 LET Y2=Y2+DY 

9135 IF X2<L1l OR X2>U1 THEN GOTO 
9155 | 

9140 IF Y2<L2 OR Y2>U2 THEN GOTO 
9155 

9145 IF NOT P THEN PLOT X2eY2 
9150 IF © THEN UNPLOT X2,Y2 

9155 REM HOLD PLACE FOR NOW 

9170 NEXT I 

9175 RETURN 


SYNCSUM = 40 


Listing 1. 


Lines 9135 and 9140 perform a useful function. Normally 
the full screen will be used for plotting, but on some occasions 
you may wish to restrict some area for text only, without any 
possibility of an intrusion from a line calculation. If the 
variables L1,L2,U1,U2 are set to 0,0,63,43 then the full screen 
will be used for plots. L1,U1 are the lower and upper limits of 


the x-axis; and L2, U2, the lower and upper limits of the y- 
axis. If you,would like to restrict the area for plotting to the 
right half of the screen for example, then set L1=31, U1=63, 
L2=0, U2=43. If this is done, then any point culculated 
outside the right half of the screen will not plot. The points 


will still be calculated, however. 


The switch from TAN A to COT A (COS A/SIN A) at PI/4 
is done to avoid the division by zero for situations where you 
have vertical or near vertical lines. The signum (SGN) function 


is used to adjust to the proper quadrant. 


14 


At this point you may ask why such overkill for drawing a 
simple line? You would be right—a line can be calculated in 
somewhat simpler fashion. A great deal of care is being taken 
with this, however, as the LINE routine will be used as a basis 
for plotting many geometric shapes, such as arcs, polygons, 
and segments. It will also be used to fill solid objects, so exact 
boundary conditions must be maintained. For now let us 
review what is needed to use the routine just presented. 
Listing 2 will serve as a driver program: 


L LET L1=0 

2 LET LZ=0 

3 LET Ul=63 

& LET U2=43 

D LET P=09 

10 CLS 

15 PRINT "INPUT XOeYO= "; 
20 INPUT XO 
25 PRINT X9; 
39 INPUT YO 
Ap PRINT ” "; YO 
40 PRINT "INPUT XləY1: "; 
45 INPUT X1 l 
50 PRINT Xl; 
55 INPUT YI 
60 PRINT ™ "3; Y1 

65 PRINT “HIT N/L TO CONTINUE" 
70 INPUT Ab 
75 CLS 

80 GOSUB 9000 

85 INPUT A$ 

30 GOTO LO 


Listing 2. 


In Listing 2 you are prompted for the starting point, X0,- 
YO, and the ending point, X1-Y1. You could also have requested 
whether or not you would like to change the screen limits, set 
by lines 1-4. 

Suppose instead of drawing a line from X0-Y0 to wherever 
we instead used X0-Y0O as the center of some shape we want 
to draw. Take for example a circle. If we let SU be the 
center and call the hypotenuse of the previous discussion the 
radius of the circle, then we should be able to calculate a 
whole series of X1-Y1 points lying on the perimeter of the 
circle by varying the angle A from 0 radians (or degrees) to 
2*PI radians (360 degrees). If we then connected these points 
with straight lines we could approximate the shape of a circle. 
The more points we calculated, the better the circle would 
look. 

Call the origin point 01 and 02 rather than X0, YO to avoid 
ambiguities. Let our convention be to draw the circle starting 
with A=0 radians, counter-clockwise through quadrants I - 
IV, until A=2*PI radians. The starting x,y point would then 


It can be shown that the x coordinate varies with the COS A 
and the y coordinate varies with the SIN A: 

X1=01+R*COS A 

Y1=02+R*SIN A 
where R is the length of the radius (hypotenuse). Furthermore 
if we divide the circle up into N sections, or segments, then 


SYNC Magazine 


kä 


we can work around the perimeter of the circle in multiples 
of A radians: 


I< =i <=N 
A = 2*PI/N 
then 


Xi=01+R*COS(i*A) 

Yi=02+R*SIN(i*A) 
Now we can develop a program to draw circles using the line 
program as a subroutine. Delete lines 1 to 90 of the Listing 2 
driver program to get a good SYNCSUM. Listing 3 is a circle 
example. 


9300 REM CIRCLE (OleO029ReNoP) 
9305 LET Al=2*PI/N 
9310 LET XO=01+R 
9315 LET YO=02 
9320 FOR J=1 TON 
9325 LET X1L=U1+R*COS (J#AL) 
9330 LET Y1=O02+R=SIN (J#A1) 
3335 GOSUB 9000 
9340 LET X0=X1 
9345 LET Yo=Yl 
9350 NEXT J 
9355 RETURN 
SYNCSUM = 32 


Listing 3. 


A simple driver program to use the circle program is found 
in Listing 4. 


l LET L1=0 
2 LET L2=0 

3 LET U1=63 
4 LET U2=43 
5 LET P=0 

D CLS 

5 PRINT "ENTER ORIGIN: 0l»02: 
20 INPUT Ql 

25 INPUT 02 

30 PRINT "ENTER RADIUS: R" 

35 INPUT R 

40 PRINT "NOs SEGMENTS/CIRCLE: 
45 INPUT N 

50 CLS 

55 GOSUB 9300 

60 INPUT A$ 

y ne a 

ae ee ee SYNCSUM = 134 


Listing 4. 


September/October 


Try playing with this function for a while. RUN it and see 
what happens as N is varied from 1 and 2 and larger. Notice 
that all the figures you see plotted are circles. Since the 
PLOT pixels are relatively coarse, lines at any angle other 
than vertical or horizontal are rather ragged, and some peculiar 
things may happen because of this. Ignoring this, you should 
be seeing what look like triangles, squares, pentagons, and so 
on until N is large enough that the polygon begins to look like 
a circle. In fact, it is never a circle but always a polygon due 
to the coarseness of the pixels, but it does approximate a 
circle. 

Instead of using an angle A let us break the angle up into 
two angles, PHI (P2) and THETA (T2) and generalize the 
circle function a bit. If we take a polygon and draw it on our 
graph paper, we could rotate it counter-clockwise on its 
origin at any angle from 0 to 2*PI radians. After 2*PI radians 
the cycle repeats. We will call this angle the inclination angle, 
PHI (P2). 

The included angle can also vary from 0 to 2*PI radians. If 
the angle is 2*PI radians, then the object is enclosed and we 
shall call it a polygon—a “generalized circle.” If the angle is 
less than 2*PI radians, then the object is not closed and we 
have an arc. Call the angle THETA (T2). A generalized 
routine is shown in Listing 5. There are some calculations 
that may not seem necessary, but they will be used later. 
Delete the Listing 4 driver program lines 1 to 65 to ensure a 
good SYNCSUM. The polygon routine will overlay the previous 
circle program if entered correctly, so these lines need not be 
expressly deleted. 


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9300 REM POLYGON/SARC (01902 aRaNe 
T2eP2¢P) 

9305 LET F=1l 

9310 GOSUB 3900 

9315 REM ENTER FROM SEGMENT 

9320 LET XO=INT (P5+01+R=COS P2) 
9325 LET YO=INT (P5+D1+RÆSIN P2) 
9330 FOR J=1 TO Nl 

9335 IF F THEN GOTO 9345 

9340 IF O2>=D1-1 THEN GOTO 9415 
9345 LET T4=J=Tl 

9350 IF ABS (T2-7T4)<=0401 THEN L 
tT T4=Te 

9355 IF J=N1l AND T3=25=P1 THEN LE 
T T4=T73 


9369 


+7T4)) 


9365 


*74)) 


9370 
9375 
93390 
7393 
97390 
7395 
9400 
9405 
9410 
9415 


9900 
9905 
9910 
2919 
9920 


LET X1=INT (P5*014+R*¥COS {P2 
LET Yi=INT (P54+02+4+R*SIN {P2 


LET X3=X1 

LET Y3=Y1 

GOSUB 9910 

IF NOT F THEN GOSUB 9750 
LET xX0=X3 

LET YO=Y3 

IF T2=T4 THEN GOTO 9410 
NEXT J 

If F THEN GOSUB 9970 
RETURN 


REM UTILITY 
LET Tl=(2*PI)/N 

LET P2=ABS P2 

LET T2=ABS T2 

IF P2>2*PI THEN LET P2= -2 


=PISINT (P2/(2*PT)) 


73929 


IF T2>zePi THEN LET TZ% «<2 


=PISINT (12/(2*PI)) 


9930 
9935 
9940 
9945 
9950 
9955 
9950 
9965 
9970 
9975 
9980 
9935 
9990 
9995 


16 


LET Uz 

LET P3=P2 
LET T3=T2 
LET P5=0.5 
LET NO=INT (P5+#T2/T1) 
LET N1=NO 
LET T2=N0*T1 
RETURN 

LET P2=P3 
LET T2=T3 
DIM X(1) 

DIM vii) 

DIM Z(1) 


Listing 5. 


Be certain to include all the lines above, as they will be 
used. Lines 9900 on are the start of the utility routines that 
will be used more extensively. Essentially what we have so far 
is a line program, a polygon/arc routine, some utility functions, 
and what appears to be some unused code. In the interest of 
brevity I will not provide a driver program until all the code is 
complete. It would be a good idea to SAVE your entries on 
tape often, in case you have problems, so you have some 
recovery point. I have found that with the 16K RAM attached 
tape reliability suffers for long files. So a good quality tape, a 
tape demagnitizer, frequent head cleaning and demagnitizing, 
several SAVEs in a row to assure a good SAVE, and lots of 
patience are needed to make LOADable tape copies. 

A segment can be visualized as looking like a slice of pie. It 
is really nothing more than an arc of less than 2*PI radians 
with two straight lines from the point of origin connecting 
each end of the arch. We can easily plot a segment by calling 
the LINE routine to draw the lines from the origin to the arc 
end points and the polygon routine to draw the arc itself. The 
routine to do this follows. The variable, F, will be used later 
when we fill the segments. For the time being assume F to be 
1. Listing 6 shows the SEGMENT routine: 


Listing 6. 


9500 REM SEGMENT (O1eO2 eR aeNeoT29P 
LPF) 

9595 GOSUB 9909 

9510 IF T2<=PI OR F THEN GOTO 95 
35 

9515 LET NL=INT (N/2) 

95920 LET LO=INT (0»55+NO/N1) 
9525 LET NO=NO-N1 

9530 LET T2=N1*T1 

9535 FOR L=1 TO LO 

9540 LET XO=INT (P5401) 

9545 LET YO=INT (P5+02) 

9550 LET XL=INT (P5401L#*R=COS P2) 
9555 LET YL=INT (P54#O02+R*SIN P2) 
9550 GƏSUB 9919 

9555 IF F THEN GOTO 9595 


99170 
9575 
9580 
9585 
9930 
3595 


+72)) 


9690 


+T2)) 


LET DO=0 

DIM X(D) 

FOR J=1 TO D 

LET X(J)=Z(J) 

NEXT J 

LET XL=INT (P5+01+RCOS (P2 


LET YL=INT (P5#024*R=SIN (P2 


SYNC Magazine 


A GOSUB to 9500 with F=1 and the other variables set as 
desired will plot a segment on the screen. The remaining task 
is to fill the segment (or unfill it) if desired. By fill, I mean to 
use the outline of the segment drawn and turn on or off all the 
pixels inside its boundaries. In this way pie charts can be 
created. 

This procedure requires two steps: first to draw the outline 
of the shape and “remember” it, and second to uniquely turn 
on each point within the shape. It is a cycle burner to say the 
least, as you will discover when you run the routine. A filled 
circle (a segment with the included angle T2 equal to 2*PI 
radians) with a radius of 20 and number of segments 24 will 
take somewhat less than 5 minutes in FAST mode! You can 
enjoy several cups of coffee if you watch it in SLOW mode on 
a ZX81. 

The approach I have used is quite simple, but, still quite 
time consuming. Using a value of F=0 for fill/unfill, the line 
routine is triggered to generate a vector of the x-y points it 
creates. When the return is made to the segment routine, it 
stores the vector Z in a new vector X or Y, depending on 
which edge it is. LINE is called again, repeatedly, to generate 
the vector of arc points. After each call, one segment at a 
time, each point in the arc vector is connected uniquely to 
the corresponding point in the X or Y vector by a call to the 
LINE routine. The line drawn is either a vertical or a horizontal 
line, from a point in Z to a corresponding point in either 
vector X or Y as appropriate. If there are not enough points 
in Z to finish the fill, an adjustment is made. The angle of 
inclination, PHI (P2), is checked to minimize redundant or 
non-connecting points. 


9605 
9610 
9615 
9620 
9625 
9630 
9635 
9640 


GOSUB 9010 
IF F THEN GOTO 9645 

LET DL=0 

LET D2=1 

DIM Y(DL). 

FOR J=1 TO Dl 

LET Y(J)=2(J) 

NEXT J 

9645 GOSUB 9315 

9650 IF F THEN GOTO 9715 
9655 IF D0=2 THEN GOTO 9695 
9650 LET ü=01 

9665 DIM 219) 

9670 FOR J=1 TO D-1 STEP 2 
9675 LET Z(J)=Y(D-J) 

9630 LET Z(J+1)=Y(D-Jel) 
9645 NEXT J 

9690 GOSUB 9750 

9695 IF NO<N1 THEN LET NL=NO 
9700 LET NO=NO-N1 
9705 LET P2=P2+T2 
9710 LET T2=NL#T1 
9715 NEXT L 

9720 GOSUB 9970 
9725 RETURN 


SYNCSUM = 168 


September/October 


It should be noted that to make life a little easier, the 
included angle, THETA (T2), is forced to be an integer 
multiple of the size of the segment angle, N. You may set it to 
whatever you wish but it will be adjusted if necessary. This 
should not be too noticeable given the coarseness of low 
resolution pixel graphics. 

A second note in using the system is this: segments are the 
only objects that will be filled. If you want to fill a polygon, 
just call the segment routine with a value for THETA (T2) of 
2*PI radians and you can create a filled polygon (or unfill an 
existing filled polygon). It is that simple. Listing 7 shows the 
remainder of the subroutine code for GRA+PIX. 


9905 
9115 
7199 
9150 
9155 


9750 
9755 
9760 
9755 


(P2>= 


LET F=1 

IF NOT F THEN DIM Z(D) 
IF F THEN GOTO 9170 

LET 2(2*I-L)=INT (X2+*P5) 
LET 2(2%1)=INT (Y2+#P5) 


REM FILL ROUTINE 

LET F=1 

LET P4=1 

IF (P2>=0 AND P2<P5*PI) OR 
PI AND P2<(1L+P5)=PI) THEN L 


ET P4=9 


S770 
9775 
97280 
9785 
9790 
9795 
9800 
9805 
9810 
9815 
9820 
9825 
96830 


FOR K=1 TG D-1 STEP 2 
LET X0O=Z(K) 

LET YoO=2(K+1) 

IF P4& THEN GOTO 9805 

IF XO<>X1 THEN GOTO 9820 
LET YL=YO 
GOTO 9880 
IF YO<>yY1 
LET X1=X0 
GOTO 9880 
IF DO=2 THEN GOTO 9855 

IF K<>1 THEN LET D9O=00-2 

IF NOT P4 AND XO<>X(DO-1) T 


THEN GOTO 9820 


HEN GOTO 9820 


9835 


IF P4 AND YO<>X(D0O) THEN GO 


TO 9820 


9840 
9845 
9850 
9855 
9850 


LET X1=X(00-1) 

LET Yl=X(DO) 

GOTO 9380 

IF K<>1 THEN LET D2=02+2 

IF NOT P4 AND X0<>Y(D2) THE 


` GOTO 9855 


9855 
GOTO 
9879 
9875 
98890 
9835 
9390 
9895 


IF 94 AND YO<>Y(D2+1) THEN 
9855 

LET X1=Y(D2) 
LET Y1=Y(92e1) 
GOSUB 9019 
NEXT K 

LET F=0 


Listing 7. 


158 


17 


1 REM GRA+PIX DRIVER MODULE 
5 DIM S$(64) 

10 LET R1=P1/180 

15 LET L1=0 

20 LET L2=0 

25 LET U1=63 

30 LET U2=43 

35 LET S=0 

40 PRINT AT 209035 

41 PRINT AT 20903;"CHANGE Liest? 
elle? FROM: "SLig™ "3L23™" "3Ul;3 
wom elas (Y/N) ?* 

45 INPUT AS 

50 IF A$="N" THEN GOTO 65 

55 PRINT AT 2090358 

56 PRINT AT 20¢0;"ENTER Llel2y 
Ul»U2:" 

60 INPUT Li 

61 INPUT L2 

62 INPUT Ul 

63 INPUT U2 

65 PRINT AT 2090355 

56 PRINT AT 20903"PLOT OR UNPL 
OT? (P/U):” 

70 INPUT A$ 

75 IF AS="P" THEN LET P=0 

30 IF A$<>"P" THEN LET P=1 

85 PRINT AT 2003S 

86 PRINT AT 20903;"LINEyPOLYGON 
AQC OR SEGMENT? (L/P/A/S)2" 

90 INPUT A$ 

95 IF A$="L™ THEN GOTO 225 

190 IF A$="P" THEN GOTO 169 

135 IF AS="A" THEN GOTO 135 

110 LET S=1 

115 PRINT AT 2090358 

115 PRINT AT 2090;"FILL (OR UNF 
ILL)? (Y/N)2" 

120 INPUT A$ 

125 IF A$="Y" THEN LET F=0 

130 IF A$<>"Y" THEN LET F=1 

135 PRINT AT Zeit 

136 PRINT AT 2090;"ENTER INCLUD 


ED ANGLE (T2) AND ORIENTATION 
ANGLE (P2) (OEGREES):" 

140 INPUT T2 

141 INPUT P2 

L145 LET P2=P2*R1 

150 LET T2=T2=*R1 

155 GOTO 180 

160 LET T2=2*PI 

155 PRINT AT 200553 

Lon PRINT AT 2090;"ENTER ORIENT 
ATIGN ANGLE (P2) (DEGREES)=" 
170 INPUT P2 

175 LET P2=P2*R1 

L30 PRINT AT 20%90;S% 

181 PRINT AT 20903;™"ENTER ORIGIN 
(91+02):" 

135 INPUT OI 

136 INPUT 02 

190 PRINT AT 20%903;S% 

191 PRINT AT 2090;"ENTER RADIUS 
{= }=" 

195 INPUT R 

299 PRINT AT 205035 

291 PRINT AT 2090;"HOW MANY SEG 
MENTS/FULL CIRCLE?" 

255 INPUT N 

210 IF S THEN GOSUB 9500 

215 IF NOT S THEN GOSUB 9300 
220 GOTON 240 

225 PRINT AT 20%70;S$% 

225 PRINT AT 2090;5"ENTER XZüe Ve 
Xl»Y1:” 

2390 INPUT XO 

231 INPUT YO 

232 INPUT Xl 

233 INPUT vi 

235 GOSUB 9090 

240 PRINT AT 2005586 

241 PRINT AT 2090;"ANOTHER SET? 
STE 

2%5 INPUT Ad 

250 IF A$<>"ĦN" THEN GOTO 35 


| een 
255 STOI SYNCSUM = 114 


Listing 8. 


The GRA +PIX routines are normally expected to be used as 
subroutines to another program, however they can be used 
from a driver program, calling the routines over and over and 
building images to gain some experience with how the routines 
and pixel graphics work. The driver routine in Listing 8 will 
prompt you for the required parameters, plot the desired 
figure, and return to you to ask for more input while leaving 
the image just plotted on the screen. If you do not like the 
image plotted, just unplot it by responding to the driver 
prompts. You can in this way build up complex geometric 
shapes on the screen. Your imagination is the limit, so have 
fun! 

Some of the code in the GRA+PIX program had to be 
written the way it appears because of some problems in the 


18 


8K Basic ROM. I think I have programmed around most of 
these errors, but there may be some cases I have not dis- 
covered. 

You need not be limited to low-res graphics. It should be 
possible to use your own character set to create high resolution 
graphics characters by creating your own 8x8 bit pattern and 
calling the video driver from RAM rather than ROM. This is 
one reason I have elected to use the TAN/COT approach for 
generating lines rather than the simpler delta x/delta y step 
method. If time permits, I will attempt to follow up with a 
method to do this. 

I would be interested in hearing comments on the use of 
GRA+ PIX, and would be happy to try to answer any questions 
if a SASE is enclosed. Pa 


SYNC Magazine 


FUZZIES & Proolems 


September/October 


construct with this many cubes? Please don’t get stuck on your 
first try! 


aa The Play School Problem 

4 = | duh ere going back to school for this puzzle, 

|| way, way back. It has been noted that, if 

| | you take three wooden cubes, or blocks, 

| | and glue them squarely face-to-face, only 

two different configurations are possible 

(see figures at the right). In our problem the reader is given 
four cubes to work with. How many different shapes can you | 


The False Scales 


cheese put into one of the scales of a false balance was found to weigh 16 
lbs. When placed in the opposite scale it weighed 9 Ibs. only. What was 
its actual weight? (From Merlin’s Puzzler by Charles Barry Townsend; 
published by Hammond, Inc.) 


The Shark Problem 


ertainly one of the most enduring forms of mechanical puzzles in the 
world is the Tangram. It has been around for hundreds of years. Below is 
pictured an oblong set of Tangram tiles. Next to it is the outline of an 
oriental fighting fish. The puzzle, of course, is to rearrange the seven Tangram tiles 
into the shape of this fish. This can be done by lightly drawing lines in the fish where 
you think the pieces should go. Don’t get hooked now; it’s not as easy as it looks. 


A Matchless Problem 


n this puzzle you must first arrange 64 matches into the figure pictured at the left. This 
figure contains 25 squares. Now comes the hard part. You must remove 32 matches so 
that you are left with just 6 squares. Can you do this in less than 5 minutes? 


The Two Numbers 


here are two numbers, such that twice the first plus the second equals 17, 
and twice the second plus the first equals 19. Find the numbers. (From 
Puzzles Old & New by Professor Hoffmann, circa 1890). 


| That’s all until next issue, folks. I hope that you enjoyed the above problems. If you have a 
| puzzle that you would like to share with our readers, please send it along. If Merlin uses it, he will 
weg ee send you a copy of one of his famous books. 
Your editor, =) RK 
Charles Barry Townsend Zhan A> ow 
Answers on page 23. 19 


4K ROM 
8K ROM 
1K RAM 


The PEEK Function and 


the POKE Command 


Introduction 

The first three articles in this series 
have all involved machine code language 
programming. This article returns to Basic 
to discuss the PEEK function and the 
POKE command. Since the 8K ROM is 
now widely available, both the 4K ROM 
and the 8K ROM are included in the 
discussion and program illustrations. 
Although this is written for the “average” 
reader, I hope that the information will 
be useful to the “advanced” reader as 
well. 


The PEEK Function 

In the operating manual the PEEK func- 
tion is described as a function that gives 
the value of the byte in memory for a 
given address. The use of the PEEK func- 
tion is demonstrated in Programs 1 and 2. 
We suggest that you run the PEEK Demon- 
strator Program at this point. 


10 FRINT "PEER DEMONSTRATOR" 

20 FRINT 

70 FRINT "ENTER ADDRESS (0-655 
oo H 

40 INPUT ADDRESS 

30 FRINT 

GO FPRINT "LOCATION 
"> CONTAINS: " 

ZO PRINT 

BO LET A=FEER (ADDRESS) 

90 PRINT "DECIMALS €a fia Uo 

100 FRINT "“HEX####4#4<''s CHR (A/16 
+23) 5CHRE( (A AND 15)+28) 5° 2" 

110 IF ĀA=1i8 THEN GO TO 130 

120 FRINT "CHRS##HHA "3 CHR CA) g” 


<"s ADDRESS: 


120 PRINT "“BINARYH#< "3 
140 LET E=128 

150 FOR C=1 TO 8 

160 IF AB THEN GO TO 200 
170 LET A=A-E 

180 PRINT "1"; 

190 GO TO 210 

200 PRINT "ron: 

210 LET B=B/2 

220 NEXT C 

30 PRINT ">" 

240 INFUT A$ 

250 CLS 


260 RUN 


Program 1: PEEK Demonstrator (4K ROM; 


1K RAM) 


Dr. I. S. Logan, 24 Nurses Lane, Skellingthorpe, 


Lincoln, LN6 OTT, U.K. This article is the fourth 
in a series. 


20 


ste ei 


PRINT "PEER DEMONSTRATOR" 
PRINT 
PRINT “ENTER ADDRESS (0-655 


INFUT ADDRESS 


) PRINT 
9 PRINT “LOCATION 


<" ADDRESS; 
"> CONTAINS: " 


A PRINT 

2 LET A=FEERK ADDRESS 

A PRINT "DECIMAL#A "sy Ag ">" 

2 PRINT "HEX######E ECHR INT 
(A/16+28) s;CHRS INT (A-INT (A146) 


e1ietce) 3">" 
IF A=118 THEN GOTO 130 


D PRINT CHRR HHH SS CHRE os": 


0 PRINT "“BINARY#H' sy 

> LET B=128 

> FOR C=1 TO B 

2 IF AB THEN GOTO 2o0o 
> LET A=A-R 

h PRINT "EIS 

d GOTO 2710 


PRINT "ons 


210 LET B=B/2 


NEXT C 
PRINT ">" 
INFUT A$ 


200 CLS 


(60 RUN 


Program 2: PEEK Demonstrator (8K ROM; 


1K RAM) 


Dr. I. S. Logan 


Next we must consider the terms ‘mem- 
ory and ‘address.’ Figure 1 shows a sim- 
plified view of how the Z80 (in either a 
ZX80 or a ZX81) is joined to ‘memory’ by 
a DATA BUS and an ADDRESS BUS. 

The ADDRESS BUS is a track that 
carries 16 binary signals in parallel from 
the Z80 microprocessor to the RAM and 
the ROM. (RAM random accss memory; 
ROM read only memory.) 

Because the ADDRESS BUS of a Z80 
system is able to carry 16 binary signals, it 
is possible to uniquely address 65536 loca- 
tions in memory. 


The addresses for these locations are: 


Binary 0000 0000 0000 0000 to 1111 
1111 1111 1111 

Decimal 0 to 65535 

Hex. 0000 to FFFF 


In the ZX80 and ZX81 systems the 
operand for the PEEK function must be 
an address in this range. Most of the 
locations will give an ‘echo’ of some other 
location as much of the possible 64K 
memory is not actually used. 

The DATA BUS is a track that carries 
8 binary signals in parallel back and forth 
between the Z80 and the memory. In the 
case of the ROM, the signals can only 
pass towards the Z80, whereas in the case 
of the RAM, the signals can pass in either 
direction. 


16 bit ADDRESS BUS 


8 bit DATA BUS 


Figure 1. 


SYNC Magazine 


Every location in the memory is also 
capable of holding 8 binary signals and 
therefore in a Z80 system a ‘byte of data’ 
can be represented by 8 binary digits which 
will have the ranges: 


Binary 0000 to 1111 
Decimal 0 to 255 
Hex. 00 to FF 


The PEEK function will therefore always 
return a value in the decimal range 0 to 
255. 


The Execution of the PEEK Function 

Let us now consider how the PEEK 
function is handled by the Basic interpreter 
in the 4K and the 8K monitor programs. 
First, take the case of the execution of 
the simple program: 


4K 8K 
PRINT PEEK (0) PRINT PEEK d 


This will print the decimal contents of 
the first location in the memory. 

For the 4K program the result will be 
33, (LD  HL,+dddd); 
for the 8K, 

211. (OUT (+FD),A). 

The line scanning part of the Basic 
interpreter when dealing with this line 
will execute the PRINT COMMAND ROU- 
TINE since the first token of the line is a 
PRINT. 

In the PRINT COMMAND ROUTINE 
(4K address: 0972; 8K address: OACF) 
the next character of the Basic line is 
considered. In the example above the 
operand for the PRINT command is the 
expression PEEK(0) or PEEK 0. This 
expression is then evaluated, and the result 
of the evaluation is stored as the ‘last 
value.’ 

In the 4K interpreter the ‘expression 
evaluator’ is found at O9E1 (Hex), and the 
‘last value’ is the system variable pair 16418 
and 16419 (Decimal). If the result is numer- 
ic, then this pair of locations will hold a 
2’s complement 16 bit number. 

In the 8K interpreter the ‘expression 
evaluator’ is found at OF52, and the ‘last 
value’ is the area of memory designated 
as MEM. A numeric result will always be 
in the form of a 5 byte floating-point 
number. 

In both cases the evaluation of the 
operand of the PEEK function is itself a 
subject of an ‘expression evaluation’ and 
the forming of a ‘last value.’ 

Once the ‘last value’ for the expression 
PEEK (0) or PEEK 0 has been calculated, 
control returns to the PRINT COMMAND 
ROUTINE where a call is made to the 
PRINT LAST VALUE ROUTINE. In the 
4K interpreter this routine is at 06F1 (Hex) 
and the operation of the routine can be 
demonstrated by using: 

RUN USR(1777). 


September/October 


This will print the ‘last value’ (in this case 


1777 Decimal). In the 8K interpreter the 


routine is at 15D7 but this cannot be 
demonstrated easily. 


The POKE Command 


In the operating manual the POKE 
command is described as being a command 
that must be followed by two parameters. 
The first parameter, which itself can be 
an expression, must give a ‘last value’ that 
can be used as an address of a location in 
the memory. The second parameter, which 
can also be an expression, must give a 
‘last value’ that is in the decimal range 0- 
255. Execution of the command will write 
the value of the second parameter into 
the location addressed by the first param- 
eter. 


10 PRINT “FOKE DEMONSTRATOR" 
20 PRINT 


30 PRINT "WT (3 shift A's) 

AO PRINT "W E (shift o: 
Sp, 5 shift oi 

30 FRINT . "MB (3 shift A*s) 

460 FRINT 


70 FRINT "ENTER & CHARACTER AN 
D NEWLINE, #HOR JUST NEWLINE TO S 


TOR" 
BO INFUT A$ 
J0 IF Ag="" THEN STOF 
190 POKE PEEK (16396) +PEEK (16397 


)*256+41, CODE (As) 
110 GO TO Go 


Program 3: POKE Demonstrator (4K 
ROM; 1K RAM) 


Programs 3 and 4 show values being 
POKEd into the display file. 


1O PRINT "PORE DEMONSTRATOR" 

20 PRINT AT 2,0; "MBB (2 shift A*s) 

TO PRINT TAB Gi B IF (shift or 
apar shitt ñ) 

40 PRINT TAR Or" (2 shift Ae) 

OO PRINT ot 6,9; "ENTER A CHARA 
CTER AND NEWLINE, ##0OR JUST NEWI I 
NE TO STOF" 

GO INFUT AS 

7O TF @$="" THEN STOF 

80 FORE PEEK 16396+FEEK 1635978 
2Jot41,CODE At 

70 GOTO 60 


Program 4: POKE Demonstrator (8K 
ROM; 1K RAM) 


In both programs the center of the box 
is defined as D-FILE +41. In the 8K ROM 
program line 80 can be replaced by: 

80 PRINT AT 3,9;CHR$ CODE A$ 
which uses the PRINT AT routine at 0918 
in the 8K monitor program to calculate 
the required address. 


The Execution of the POKE Command 
The syntax for the POKE command is: 
POKE (expression) (,) (expression) 

and this is checked by referral to the 

syntax table. 
In the 4K ROM the appropriate entry 
is seen in Listing 1 and in the 8K ROM in 

Listing 2. 


FUN in 1K from SSL 


Parrot 


builds amazingly funny random sentences. 


don’t want to. Comes with 


documentation. 


Subhunter 


TV screen ocean. 


must predict the sub’s 


a 

| 

B 

| 

g 

| 

E 

- experience included. 

Arith-1 Du 

addition and subtraction 

= 

l 


included. 


Microartist 
reverse video graphics choosing 
memory. 


programming language 


T0 O R D E R : All prices include shipping and include 
documentation of the program, its desim, and its use. Send check or 
money order payable in U.S. dollars (sorry) to: Systems and 


- Given names, actions, and places (or other phrases), it 


Good progran to study Basic programming. 


- zët LIVE ACTION GAME rs of submarine warfare on a 
You are the hunter-killer of elusive submarines. 
Since your torpedos are slow and the targets are rarely detected, you 
course. 


- Grades responses to generated lists of 
problems 
comments on the accuracy of the player. 


- Allows you to draw pictures using normal and 
and placing symbols to the limit of 
This is a mini programming language. 
interperter 
introduction as well as generating interesting graphics. 


Let the Parrot say what you 
phrases and 


$5 (£3) 


initial set of 


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$10 (£5.50) 


Multiple 


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of nuabers 


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Multiple lengths 


Documentation explains 


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Solutions, Ltd., 5054 Kenerson Drive, Fairfax, Virginia 22032 U.S.A. 


| SRSA CH vr SS Ce E ER BB E S S L EES SE Se aaa Si Sl E a 


21 


In the 4K ROM the appropriate entry is: 


Address Contents 


07A4 06 
07A5 D8 
07A6 05 
07A7 D1 
07A8 09 


Comment 
The first expression is of type ‘6’. 
The ‘comma’. 


The second expression is of type ‘S’. 
The address of the POKE COMMAND 


ROUTINE is 09D 1. 


In the 8K ROM the appripriate entry is: 


19 
20 
30 
40 
30 
60 
70 
BO 
99 
100 
110 
120 
130 
140 
150 
160 
170 


180 
190 
200 
219 
2229 
230 
240 
250 
260 
320 


270 


280 
on 
290 
TOO 
SLO 


320 


330 
340 
350 
360 
370 
AGO 
390 


400 
410 


420 
430 


22 


Address Contents 


0C80 06 
0C81 1A 
0C82 06 
0C83 ` o 
0C84 92 
0C85 0E 

RANDOMISE 

GO TO 1190 

FRINT “PELMANISM" 

FRINT 

PRINT “HERE ARE THE CARDS" 

FRINT 

FRINT C$ 

PRINT “1.2.3.4.5.6. 7.8." 

FRINT 

RETURN 

LET C$="? 7 7 7 7 7 7 "an 

DIM A(8) 

LET F=0 

FOR B=38 TO Ai 


FOR C=1i TO 2 

LET D=RND (8) 

IF NOT A(D)=0 THEN GO TO 16 
Q 

LET A(D)=B 


NEXT C 
NEXT B 

GO SUB 30 
GO SUB 370 
LET G=F 

GO SUB 379 


IF F=G THEN GO TO 230 
IF NOT A(G)=AC(F) THEN GO TO 


LET B=-—1+PEEK (16392) +PEER (1 
6393) K256 
IF FEERK (B+G6X*2)=0 THEN GO TO 


FOKE B+Gxk2,0 
FOKE B+Fx2,0 

LET F=F+i 

PRINT F; "#F AIRS FOUND, FRES 
S N/L" 

IF F=4 THEN GO TO 420 

INPUT A$ 

CLS 

GO TO 210 

FRINT "CARD#"s 

INFUT F 

IF Fei OR EB THEN GO TO 38 
© 

PRINT F;"#IS A -#";CHR$(A(F 
)) 

RETURN 

CLS 

FRINT#, "WELL DONE" 


Comment 


The first expression is of type ‘6’. 
The ‘comma’. 

This time, again type ‘6’. 

No further requirements. 


The address of the POKE COMMAND 


routine is 0E92. 


Comment 

A good idea. 

Jump past display. 
Title 


The cards. 


The numbers of the cards. 


Eight cards; face~-down. 
Value of cards. 


Fair counter initialised. 
Will be cards A,B,C % D, 


Form a pair. 
A card. 
Already assigned’ 


Assign value to card. 
Next of pair. 

Next value. 

FRINT BOARD. 

INFUT ROUTINE. 

Copy mumber of first. 
INFUT ROUTINE 

They were the same! 
Are they a pair’? 


Find the card in C$, 
in the variable area. 
Fair already chosen? 


Remove the cards from 
the board. 

Score the pair. 

The status report. 


All over? 
Wait for N/L. 


Back for next try. 
INFUT ROUTINE 

The chosen card, 1-8. 
Validity test. 

The value of the card. 


Return with card F. 


The point of success. 


Readers who have larger memories might like to increase the number of 
cards on the board by changing lines 80, 110, 129, 140 (increase 41 to 
reflect the number of pairs), 160, 330 (number of pairs), and 390. 


Program 5: Pelmanism (4K ROM; 1K RAM) 


In the POKE COMMAND ROUTINEs 
the actual POKEing is done with the 
following lines: 


Address Menmonic 


4K: 09DF LD (DE),A 
8K: UE A3 LD (BC),A 


Note that in both cases only a single byte 
is loaded into a memory location. 

Here is a simple game that uses the 
features discussed in the main body of 
the article. 


Pelmanism 

This game is usually played with a pack 
of playing cards. The cards are placed 
face-down on a table and the player, or 
players in turn, take two cards and look 
at them. If the cards are of the same 
value, then the player scores 1. If the 
cards are different, then they are 
replaced. 

The game is therefore one of memory. 
In the programs 5 and 6 below the cards 
are kept in string C$, and cards that have 
already been found to be pairs are removed 
from the string using a POKE operation. 

The author would be pleased to see 
any programs that have been written fol- 
lowing the ideas mentioned in this article. 


Fa 


SYNC Magazine 


—- Qo wy 


10 RAND 
20 GOTO 80 

30 PRINT "PELMANISM" 

40 PRINT AT 2,0;"HERE ARE THE 

CARDS" 

SO PRINT AT A, OC 

60 PRINT "1.2.3.4.5.6.7.8" 

70 RETURN 

BO LET Cee"? 9 

90 DIM A(B) 

100 LET Peo 

110 FOR Besa TO 41 

120 FOR C=1 TO 2 

130 LET D=INT (RND&S+1) 

140 IF A@(D)<20 THEN GOTO 130 
iSO LET @(D)=B 

L60 NEXT Č 

170 NEXT B 

160 GOSUB ZO 

190 GOSUB 340 
200 LET Get 

210 GOSUB SSO 
220 IF F=G THEN GOTO 200 
250 IF A(G LHA) THEN GOTO 290 
240 LET B=1+PEEK 16400+4FPEEK 164 
OI 
250 IF PEEK (B+G*2)=0 THEN GOTO 


260 FOKE B+Gxk2,0 
270 POKE B+F x2, 0 


270 FRINT Fs "#PAITRS FOUND, FRES 
S N/L" 

SOO IF F=4 THEN GOTO 400 

S10 INPUT A$ 

me CLS 

on! GOTO 180 

240 PRINT 

A0 PRINT "CARD" 5 

360 INFUT F 

S70 IF F<i OR Fog THEN GOTO 360 

380 FRINT Fs "#15 A ~-#"sCHRE ACF 
) 

370 RETURN 

400 CLS 

410 FRINT TAB 8; "WELL DONE" 


Comment 

A good idea. 

Jump past display. 
Title. 


The cards. 


The numbers of the 


Eight cards, face-down. 


Value of cards. 


cards. 


Fair counter initialised. 
Will be cards A,B,C & D. 


Form a pair. 
A card. 
Already assigned” 


Assign value to card. 


Next of pair. 
Next value. 
PRINT BOARD. 
INFUT ROUTINE 


Copy number of first. 


INFUT ROUTINE 


They were the same! 


Are they a pair’ 


Find the card in C$, 


In the variable ar 


OA. 


Fair already chosen? 


Remove the cards from 


the board. 
Score the pair. 
The status report. 


ALL ØYER T 
Wait for Nat, 


Rack for next try. 


INFUT ROUTINE 


The chosen card, 1-8. 


Validity check. 


The value of the c 


Return with card F. 


The point of success. 


Program 6: Pelmanism (8K ROM; over 1K RAM) 


Note that in this program the first card is at: 
“1+PEEK 16400+PEEK 16401*256” 


BuUZZie answers 


The Play School Problem: Eight different shapes 
are possible. 


The False Scales: The answer is 12 lbs. Problems 
of this class are solved by ascertaining the 
square root of the product of the two weights. 
In this case 9 x 16 = 144, and the square root 
of 144 is 12, the required answer. 


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The Two Numbers: The required numbers are 
5 and 7. For if twice the first + the second = 
17, and twice the second + the first = 19, then 
the sum is 36. This is the same as three times 
the first + three times the second. The sum of 
the numbers themselves must be 36 + 3 = 12. 
Since twice the first + the second is an odd 
number, the second is also an odd number, and 
the first, being the even number 12 less an odd 
number, must also be an odd number. Now the 
only pairs of odd numbers which together make 
12 are 1 and 11, 3 and 9, 5 and 7. Of these, we 
find by experiment that 5 and 7 are the only 
two that answer the conditions: 5x 2 + 7 = 17, 
and7x2+5= 19. 


23 


4K ROM 
1K RAM 


The Need for a READ 

READ is a very useful statement. FOR- 
TRAN has it, and so do the Hewlett- 
Packard Basics. Microsoft, the company 
that wrote the Basics for most of the 
small American computers, has provided 
READ statements in its languages. How- 
ever, the ZX80 does not have it. This is 
the one statement that I have missed more 
than any other in the Sinclair 4K Basic. 

INPUT works fine if the program needs 
different data every time it is RUN. For 
example, a program to balance your 
checkbook would use INPUT to get the 
information about the check you wrote 
today. But many programs require large 
quantities of unchanging data in their 
arrays before they do their things. A lot 
of game programs fall into this category 
and so do some industrial control pro- 
grams. This is normally the job of the 
READ statement. 

In a game program, for instance, an 
array would be created by a DIMension 
statement, and then the necessary data 
would be READ into each element. In 
Basic it would look something like this: 


10 DIM A(50) 

20 FOR J=0 TO 50 

30 READ AA 

40 NEXT J 

50 DATA 174,39,317,255,78,131, 
286,228,224, 152,158,186,247,241, 
85,161,24,145,50,271,38,106,165, 
95,313,206,95,261,80,58,259,296, 
24,1,178,133,268,41,249,250,279, 
294,66,323,179,115,81,66,93,200, 
281 


Listing 1. 

A READ statement as it might look on the Sinclair 
if it had one. 

This part of the program would first open 
Space in memory to store an array named 
“A” and having fifty-one storage locations 
(from A(0) through A(50) inclusive). It 
would then initialize A(0) with the value 
174, A(1) with 39, A(2) with 317, and so 
on until it placed 281 into A(50). 

Of course, there are ways to get around 
the READ deficiency. We could eliminate 
line 50 and change line 30 to: 

30 INPUT A(J) 

Then we would hand our friends a list of 
fifty-one numbers to type in each time 
that they wanted to play the game. Some- 
how, I think this would kill much of the 
fun! Furthermore, this way is sensitive to 
errors. Sometimes a program can be 
completely spoiled by a single error. 


Edward A. Kennedy, Jr., 16 701 Red Oak St., 
Bensenville, IL 60106. 


24 


Machine Language Teaches 
the ZX80 to READ 


Edward A. Kennedy, Jr. 


A better substitute for our missing 
READ statement would be: 


20 LET A(0)=174 
30 LET A(1)=39 
40 LET A(2)=317 


50 LET A(3)=255 

60 LET A(4)=152 
and so on until: 

510 LET A(49)=200 

520 LET A(50)=281 


Listing 2. 
Initializing an array without a READ statement. 


This would work! The data would be 
permanently in the program and the 
possibility of errors occurring each time 
you ran it would be eliminated. It has two 
disadvantages. It requires a lot of typing, 
and it ties up two-and-a-half to three times 
as much memory as would have been 
required if we had the READ statement 
to work with (as in Listing 1). The program 
of Listing 1 would require 221 bytes 
assuming that DATA and READ were 
one-byte keywords. On the other hand, 
the program of Listing 2 would require 
644 bytes to get the same fifty-one numbers 
into the same fifty-one array locations. 

So I decided to create a subroutine 
that would function a lot like the READ 
statement does in the native machine 
language of the Z-80 CPU (Central Pro- 
cessing Unit), and I could get at it with 
the USR function, when I needed it. 


Using the USR 

The ZX80 has a “USeR” function that 
tells the machine to do a machine language 
subroutine beginning at any place in 
memory that the programmer chooses. 
Suppose that you had a machine subpro- 
gram starting at memory address 14,336. 
Also suppose that this subroutine had to 
give us back some information. You might 
write the following: 


ZO sis 
220 LET INFO= USR(14336) 
230 xs 


When the machine went to execute line 
220, it would first run the USR subroutine 
and give back a number. 

The Z-80 CPU has many internal loca- 
tions in which it can store numbers that it 
is working on. We call these internal 
storage cells “registers.” When the com- 
puter comes back from running the sub- 
routine, it would still have one more thing 
to do with line 220. It would have to copy 
the number in two of its registers into the 
variable named INFO. The new value of 
INFO would be equal to the value of the 
H and L registers (taken as a pair) at the 
instant that the machine language sub- 
routine was completed. 

This means that when I wrote the READ 
subroutine, I had to make sure that the 
number it was READing got into the HL 
register-pair before the Z-80 found the 
instruction to RETurn from the subroutine 
to the execution of the Basic line that 
called it. Keep this in mind if you plan to 
write subroutines of this type. 

The programs in Listings 3 and 4 show 
what the USR function looks like from 
the programmer’s point of view. 


60 LET INFO=USR(16430) 
70 PRINT “THE VALUE OF USR 
=” INFO 


Listing 3. 
USR returns the number 16430. 


Line 1 is the REMark line where the 
machine code will be stored. The first 
thing that happens when you run this 
program is that line 10 POKEs 201 into a 
location in line 1. That number, 201, is 
the whole subroutine! It is the decimal 
form of the instruction telling the Z-80 to 
RETurn. 

After line 10 puts the instruction into 
memory, line 60 tells the computer to go 
to the exact same spot and do whatever 
commands it finds there. But the Z-80 
finds RET at the first location. So it makes 


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25 


no changes whatever; it simply comes 
back to the Basic program. Then it takes 
whatever number it finds in the HL register 
and puts a copy of it into the variable 
named INFO. When RUN, this program 
gives: 


THE VALUE OF USR= 16430 


This is the number that was in the HL 
register! It is also the number of the 
location where the subroutine starts. This 
tells me that the computer probably uses 
the HL register to help it get to the 
subroutine in the first place. 

Now when I look at the program again, 
I notice that line 1 has changed. One of 
the dashes has changed to a question mark. 
That is because the POKE changed the 
contents of one of the memory locations 
being used to store line 1. Before we ran 
the program, that cell held number 220. 
When the computer looks up 220 in its 
table, it finds that it must display a dash. 
However, when it looks up the 201 that 
we put there instead, it finds that no display 
character has been assigned yet. So it 
jumps to an error routine and prints a 
question mark. There are twenty-five 
different numbers which can produce that 
question mark when POKEd into line 1. 
Typing a question mark is equivalent to 
POKEing the number 15. So if I want one 
of the others, I must use the POKE 
statement as I did here. 

One of the most important things to 
understand about this method is that a 
number stored in that location can mean 
different things to the system at different 
times. That same 201 can be a low level 
instruction to the processor, or it can be a 
number that must be interpreted and 
transferred to the display file. Under 
different circumstances, it might even have 
been a statement in Basic that the machine 
would have to look up and execute. In 
each case the action is different. 

Let me expand that program a little! I 
have not shown that the value of the HL 
register-pair becomes the value of USR. 
The following lines added to Listing 3 
begin to do that. 


1 REM---?------ 
10 POKE 16430,33 
20 POKE 16431,0 
30 POKE 16432,0 
40 POKE 16433,201 
60 LET INFO=USR(16430) 
70 PRINT “THE VALUE OF USR 
=” INFO 


Listing 4. 
USR will equal the value in 16431 plus 256 times 
the value in 16432, unless 16432 is more than 127 
in which case USR will be negative. 


26 


The Z-80 recognizes the decimal num- 
ber 33 (which line 10 will now place in 
memory) as the instruction to put the 
number that follows it in its L register, 
and the one after that in its H register. 
(When taken together, L is the lower part 
and H is the higher part of the pair.) 

If you RUN it now, you will be told: 


THE VALUE OF USR= 0 


Zero is the number we told it to put in the 
HL pair! If you doubt it, change line 20 to 
POKE different numbers at that location. 
If you use values from 64 through 127, 
however, you stand a strong chance of 
confusing your computer so thoroughly 
that you might lose your program. For 
the moment, you will probably want to 
stick to the values from 0 through 63, and 
from 128 through 255. 

I was fascinated by the changes in line 
1 when I put different codes in it. The 
“Character and Keyword Appendix” of 
the users manual gives details of what 
each number stands for. 


Supporting the Effort 

By now, you can see that programming 
in machine code on the ZX80 is not the 
easiest thing in the world. Typing in all 
those POKE statements is difficult enough 
for a subroutine that occupies only four 
bytes, so imagine what it would be like 
for a program that filled 159 bytes as our 
READ subroutine does! 

A Word about Hexidecimal 

Another difficulty is that each variation 
of each instruction that the Z-80 has 
corresponds to one or more numbers. In 
order to know which number(s) I need, I 
have to look at a table. These tables are 
written in either a binary number code or 
a hexidecimal number code. I find the 
hex tables easier to use. 

Since the ZX80 requires a decimal 
number code for its POKEs and returns a 
decimal number when it does a PEEK, it 
is up to us to do some converting. 

The hexidecimal number system has 
sixteen possible numbers that can be put 
in any position: 


0, 1, 2, 3, 4, 5, 6, 7, 8,9, A, B,C, D, E, & F 


Remember that A, B, C, D, E, and F are 
not letters here; they are numbers just 
like 8 and 9 are numbers. 

For instance, the hexidecimal form of 
the instruction LD HL,NN, used in Listing 
4 to get a number into HL, is 21. That is 
not twenty-one because it is not two tens 
and a one. It is two sixteens and a.one, or 
the same as thirty-three in decimal. 


The hexidecimal table lists the number 
for RETurn as C9. This means that there 
are C times sixteen plus nine times one. 
Since C equals 12, multiply 12 by 16 and 
add 9: 


(12x16) + (9x1) = 201 


In Listing 4 you will see that line 10 POKEs 
33 and line 40 POKEs 201. These are 
exactly the values just computed. 
Making It Automatic 

When only three or four numbers are 
involved, this is not too demanding, but 
doing 159 numbers is another matter. 
Fortunately, a program can be written in 
Basic to eliminate the need for all those 
POKEs and conversions. Listing 5 gives 
such a program that will run on 1K. While 
it looks short, it runs into trouble if it tries 
to display all 159 bytes of the machine 
program. So, after you type in the 105th 
entry, it takes a moment to erase the 
screen so that you have room to finish the 
subroutine. 

If you are running the program and 
want to stop, type S and then NEWLINE. 
To start again, type CONTinue and NEW- 
LINE. When you do, the program will 
PEEK at all the locations that were on 
the screen before you stopped, convert 
them to hex, and display them again. So 
you will pick up exactly where you left 
off. 

If, on the other hand, you find that you 
made a mistake five bytes back, you will 
first need to stop the program as above. 
Then you type in: 


LET I=I-5 


followed by NEWLINE. Then, when you 
start the program again, you will be five 
spaces back and ready to make the needed 
correction. The same is true if you want 
to look at the next twenty locations. Stop 
the program, add twenty to “I”, and then 
press CONTinue and NEWLINE. 

When you are entering code with this 
program, you must type in both numbers. 
The ZX80 will not supply a missing zero. 
If you want 00, you must type 00 and not 
0. A single zero will be entered as the hex 
number E5, and that is not the same at 
all. 


Conclusion 

In this article I have discussed what a 
READ statement does and why it is handy. 
The subroutine given above will duplicate 
the action of the READ statement, but it 
must be stored in a REMark to protect it 
and to allow us to SAVE it. The USR 
function is the means of retrieving the 
material in storage. Finally, a 1K program 
enables you to put material into the stor- 
age. 


SYNC Magazine 


1 REM --~---------------------- 3160 minus signs reserve space for machine 
Aaea ea NES H codes 
ee EO EE EN IN AS AEH OR ID ; 23 in first line 
FS e IE I OE A SES ER ; A in each of the next four lines 
a eee H and 9 in the sixth line 
2 DIM UCI? Machine subroutine uses U(O) for address 


A LET U(O)=16600 5 
3 LET R=16427 


of next DATA and U1) as a flag 


50 FOR I=R TO 16585 
60 IF I-R=105 THEN GO TO 160 
70 INPUT C$ 

80 LET C=CODE (C$) 

90 IF C=56 THEN GO TO 150 

100 IF Cé28 OR C>43 THEN GO TO 
70 

110 PRINT C$;" "; (2 sp.) 

120 POKE I, 16*(C-28) +CODE(TL#(C 
$))-28 

130 NEXT I 

140 GO TO 999 


150 STOP 

160 CLS 

170 LET S=R 

180 IF I>R+104 THEN LET S=R+80 
190 FOR J=S TO I-i 

200 LET K=FEEK (J) 

210 LET L=K/16 

220 PRINT CHRS(L+28) ; CHR (K-Lx 
16)4+28;" "3 (2 sp.) 

230 NEXT J 

240 GO TO 70 

999 STOF 


Start and end of machine code storage 
Do make room in the display for the rest 
; Enter machine code 


If it was an "S" then go to "STOF" 
Ir not hexidecimal go back and try again 


¿Else display it with two spaces after it 
s Then convert and POKE it 


;AVOid running over 


3;Fortion of routine displays codes that 


; are actually stored in memory 
If too many locations will be displayed 
8 delete first 80 and display the rest 


sLook at the number in this location 
;Convert it and 

` convert some more and display it 
: do not forget the two spaces 


Listing 5. 


Short (1K) version of Basic program accepts and converts hexidecimal 
machine code and stores it in its own line 1. (Enter “S” to STOP!) Hey 
codes between 40 and 7F can scramble the system when put in a REMark 
line, and must be avoided unless lines 5 and 50 are changed to store the 
codes where they will not be displayed. 


To anticipate, Part 2 will present the 
READ subroutine and explain more about 
the “forbidden” codes, methods of getting 
along without them, and some of the 
features of the system. 

For readers interested in more detailed 
study, I suggest the following works: 

Barden, William, Z-80 Microcomputer 
Design Projects, Indianapolis: Howard 
Sams & Co., 1980. This book has me 
excited. It shows how to make a manual 
EPROM programmer and a small dedi- 
cated computer with software for several 
projects. 

Barden, William. The Z-80 Microcom- 
puter Handbook, Indianapolis: Howard 
W. Sams & Co., 1978. Good for its clarity 
and organization. 

Nichols, Elizabeth A.; Nichols, Joseph 
C.; and Rony, Peter R. Z-80 Micropro- 
cessor Programming and Interfacing. 2 
books. Indianapolis: Howard W. Sams & 
Co., 1979. Book 1 has the most complete 
tables. Both volumes fill certain other gaps. 
They give a number of experiments that 
apply to an Italian computer. 

Zaks, Rodney, How to Program the Z- 
80. Berkley, CA: Sybex, 1979. This is a 
624 page monster, but it seems exceedingly 
clear. It devotes an incredible 284 pages 
to the Z-80 instruction set. a 


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CN Geig NI Ate ONE 
iv nez A i NZ avo OST" 


7 EL 


E + 


Schematic for Sinclair 


16K RAM Pack 


SYNC Magazine 


28 


Using Key and Token Expressions 


While translating a TRS-80 program 
into a ZX80 program, I crashed the system. 
I had already saved most of the program, 
so I loaded it again and proceeded to cut 
anywhere possible to save memory. When 
the program was as compact as I could 
get it, I ran it again. After a few inputs the 
program stopped. I quit for the day. 

A couple of days later, I was writing 
directions for a game in a REM statement 
and accidentally pressed the shift key and 
the “/” key simultaneously. Instead of 
“/”, “NOT” appeared! I experimented more 
with this new technique and discovered 
that keywords as well as tokens could be 
typed into program lines in full—spaces 
and all—with practically a single key- 
stroke. 


Richard W. McDaniel, Box 71, Glasgow, VA 
24555. 


Richard W. McDaniel 


This technique not only saves typing 
time, but, because a keyword or a token 
is usually stored as a single byte, it also 
saves memory. I went back to the program 
I had been translating and modified it 
with this technique. It ran perfectly. 

Let us look at some examples of how 
the technique works. 

The program line: 

10 REM TO RUN, USE GOTO 100 
written the ordinary way takes 24 bytes 
whereas with the above key and token 
technique it only takes 14 bytes, for a 
saving of 10 bytes. A line such as: 

20 PRINT “ENTER YOUR NAME” 

can be 

20 PRINT “INPUT YOUR NAME” 

for a saving of 4 bytes. 

In a line like 
30 LET Z$=“JIM AND JOE“ 
you save 8 bytes by using the token 
“AND”. 


= INVENTIVE PROGRAMS FOR THE ZX80 4K/1 


| PARTIAL LIST OF 50 4K/1K TITLES IN STOCK 
* FLIP-A-COIN - Demonstrates 50-50 chance 


* 1 KEY BANDIT - Our 3-wheel slot machine pays out wi 


To use the technique in a line such as 
100 PRINT “TO STOP PROGRAM, 
INPUT S” 
type the statement number. Next type the 
last keyword first; then back up using 
shift “5” and enter the next to last keyword 
and so on until all keywords are entered. 
After that, type the keyword that uses the 
keyworded-characterstring either REM, 
PRINT or a characterstring, then type 
the tokens in their respective places. Finally, 
type any alphanumerics. The technique 
used in the above line saves 9 bytes. 

If the keyword or token is preceded by 
another keyword or token, the preceding 
space of the following expression is omitted. 
If there is an alphanumeric between key- 
words or tokens, the spaces of each remain 
the same. More information can be found 
on page 105 of your ZX80 operating 
manual. I hope you find this technique as 
useful as I have. Be 


* TURRET GUNNER - Blast away at the enemy aircraft (MCD) w 
* GUILLOTINE - Your brain is tested for math ability w 

* BLACKJACK - Featuring credit betting and winnings wi 

* KEYBOARD GRAPHICS - The cursor leaves behind any chr. 

* BARRAGE - Artillery against a city that shoots back w” 

* ZX80 BASIC TEST - 2 sets of questions on 1-key entry 

* SCORES IN REM/3x3 MOVES-POKES - Routines for your games 
* FOIL FENCING - Test your reaction time at 100 levels wi 


These are priced at $1.00 each and ALL of our listings are 
guaranteed to run within 1K RAM if entered exactly as instructed. 
Also, each listing includes statement comments explaining program 
flow. If you prefer to have a selection from this ad on tape, add $5.00 
recording fee - listings will be documentation. 


TO ORDER 


Specify either 10 GAMES PAK or the selection of printed listings 
from this ad and enclose payment with $2.50 Shipping and Handling. 
(SC residents add 4% tax before S&H. Orders paid by Money Orders 
sent soonest; please allow 4 weeks for checks. Full catalog sent with 
order or just write for one. MCD=Machine Code Display) 


10 GAMES PAK (on tape) - ONLY $17.50 


The six checked above plus four of our BEST on cassette: 
* BOMB RUN - Watch your bomb as flak zeroes in on you (MCD) $3 
* ARCADE INVADERS 2 - Our version of the coin-eater w/score (MCD) $3 
* FLYSWATTER - An original ZETA game to test your eyes (MCD) $3 
* WORMHOLE - “Black Hole” with a star-reversion timer (MCD) $3 
(Total listings price plus recording fee is $23.00. This introductory price 


of $17.50 includes the printed listings of all 10 programs on the tape, 


but don’t delay -- this offer expires Nov. 30, 1981). 
ZETA SOFTWARE / P.O. Box 3522 / Greenville, S.C. 29608-3522 


September/October 


HARDWARE 


Keyboard Sounders 
Every keyboard entry gives 
you a short audible bleep. 
KS1 for ZX80 

KS2 for ZX81 

Tape Recorder interface. 
Gives adequate level for 
loading from cassette 
machines. 

T.R.I. for ZX80/81.....£12 
Video Amplifier Unit 

Will drive standard 1 volt 
monitors. 

NAU for ZX80/81 .£12 


Complete with leads and diagrams. 
Connections only take a few minutes. p-p. sop 


D. BRUCE ELECTRONICS 

THE BEACON BLACKHALL ROCKS 

CLEVELAND TS27 4BH 
Tel: 0783-863612 


29 


4K ROM 
1K RAM 


In Cannonade you are the commander 
(choose your own rank) of a squad of six 
men. You have been given as your next 
objective the capture of an enemy gun 
emplacement. Your men must outman- 
euver the gun’s handlers. If they are spotted 
as they are advancing, they may be fired 
upon. When a man is hit, he cannot return 
to his base until the gunner is distracted 
and fires on another target. Should one of 
your men breach the fortification protecting 
the emplacement, the gun is silenced and 
the position is taken. 

Since the game program is long, a tem- 
porary program is necessary to initialize 
certain variables so that the program will 
run in 1K. Enter the program in Listing 1, 
RUN it, and then delete lines 10 to 120 
inclusively by typing the line number and 
NEWLINE. 

Now you can enter the main program 
(Listing 2). SAVE it as soon as you have 
finished entering it. Do not RUN it because 
RUNning will alter the values stored in 
the variables initialized by the program in 
Listing 1. To play the game enter GOTO 
100. 

The prompt will ask you which man 
you wish to move. Enter a letter from A 
to F and NEWLINE. The letter on the 
screen, corresponding to the man you 
have chosen to advance on the emplace- 
ment, will move forward a random distance 
and may move either up or down one line 
on the screen. If he is fired upon and hit, 


Drew Nisbet, 6 Moffatt Crt., Toronto, Ont., Canada, 


M9V 4F1. 


30 


Cannonade 


10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
110 
120 


100 
110 
120 
130 
140 
150 
160 
170 
180 
190 
200 
210 


Drew Nisbet 


LET IT = 4 

LET D = O 

LET A = 0 

DIM L{20) 

DIM M(6) 

DIM P(6) 

LET L(20) = 2 
FOR I = 1 TO 6 
LET P(I) = 1 
LET M(I) = I 
If I > 3 THEN LET M(I) = M(I) + 1 
NEXT I 


Listing 1. 


RANDOMISE 

CLS 

FOR I = 1 TO 7 

FOR K = 1 TO 19 

LET L(K) = O 

NEXT K 

PRIINI 33” Ze 

FOR J = 1 TO 6 

IF NOT M(J) = I THEN GO TO 240 
IF L(P(J)) = O OR L(P(J)) = 2 THEN GO TO 220 
LET P(J) = P(J) + 1 

GO TO 190 


Listing 2. 


SYNC Magazine 


the letter will appear in inverse video. It 
will remain this way until another man is 
fired upon by the gunners; then the man 
can return to the base. This is shown by 
the return of the letter to the left side of 
the screen. When a man has broken 
through the line on the right side, the gun 
has been captured. The number of moves 
required will then be displayed. To end 
the game before the gun is captured, press 
NEWLINE when the prompt calls for a 
letter. The number of moves made up to 


The game is relatively short, but, if you 
want to increase the difficulty and conse- 
quently the playing time, decrement the 
values which determine the distance moved 
by changing line 420. 

In order to replay the game, you must 
reload the program from the tape because 
of the method by which the variables 


this point will be displayed. 


were initialized. 


Cannonade 


220 
230 


LET L(P(J)) = J + 37 
IF D = J THEN LET L(P(J)) = J + 165 


240 NEXT J 

250 FOR K = 1 TO 20 

260 PRINT CHRS(L(K)); 

270 NEXT K 

280 LET L(20) = 2 

290 IF NOT T = I THEN GO TO 310 

300 PRINT “SEE NOTE AT RIGHT”;I; NOTE: 

310 PRINT 

820 NEXT I PRINT CHARACTERS FOR 
330 PRINT LINE 300 ARE: 
340 FOR I = 1 T0 6 

350 IF P(I) = 20 THEN GO TO 620 1. SHIFTED “G” 
360 NEXT I 2. SHIFTED “A” 
370 PRINT “MAN:” 3. SHIFTED “D” 
380 INPUT A$ 4. SPACE 

390 IF A$ = “” THEN GO TO 630 

400 LET X = X + 1 

410 LET Q = CODE(AS) - 37 

420 LET P(Q) = P(Q) + RND(5) + 3 


430 
440 
450 
460 
470 
480 
490 
500 
510 
520 
SEI 
540 
550 
560 
570 
580 
590 
600 
610 
620 
630 


IF P(Q) > 20 THEN LET P(Q) = 20 
LET J = RND(3) 

IF J = 1 THEN GO TO 510 

IF J = 2 THEN LET K = -1 

IF J = 3 THEN LET K = 1 

LET I = M(Q) 

IF I + K = 0 ORI + K = 8 THEN GO TO 440 
LET M(Q) = I+ K 

IF RND(3) = 2 THEN GO TO 100 

LET P(D) = 1 

LET D = 0 

LET K = 0 

FOR I = 1 TO 6 

IF P(I) < K OR D = I THEN GO TO 600 
LET K = P(I) 

LET D = I 

LET T = M(I) 

NEXT I 

GO TO 100 

PRINT “GUN CAPTURED IN “; 

PRINT X;” MOVES.” 


September/October 


Blank Cassettes 


The quality of cassette tape used to 
Save and load programs is an important 
factor in getting the programs to run. 
Tape quality for computers is measured 
differently from quality for audio tape. 
The tape must be capable of sending to 
the computer the electronic signals of 
the program without transmitting extra- 
neous noises that could interfere with the 
ability of the computer to load the tape. 

Our blank cassettes are tested and 
recommended for computer use. C-10 
cassette, 5 min. per side, blank label on 
each side in a Norelco hard plastic box. 
[0010] $1.25 each. 


Head Cleaner 


After hours of use, the read/write head in 
a cassette recorder will pick up minute 
particles of tape oxide. This dirt will hardly 
be noticable in dictation or music. But it is 
very noticable in computer use. One dropped 
bit in 16,000, and the program won't load. 

Help keep your recorder in top shape 
with our non-abrasive head cleaner. It consists 
of 18 inches of stiff cleansing fabric:in a 
standard cassette sheli. One 10-second pass 
every 40 hours of use will keep your heads 
as good as new. [0011] $2.00. Send pay- 
ment plus $1.00 Shipping per order to: 


Peripherals Plus 


39 East Hanover Avenue 
Morris Plains, NJ 07950 


ZX81 MINI 
INVADERS 


ALL THE THRILLS OF ITS BIG 
BROTHER ON A 24x16 DISPLAY ALL 
IN 1K RAM. £4 for M/C CODE CASSETTE 


ALSO TV GAMES (16K RAM) 
ZX 81 INVADERS 
ZX 81 GALAXY WARS 


m/c code routines with continuous non- 
flicker display & fast moving graphics £4 
each cassette. 


J EDMONDS, 29 Chestnut Ave. Grays, Essex 


Too Much! 


How can we tell you 
about 200 products 
in one advertisement? 


Our new catalog gives detailed 
descriptions of over 200 peripherals. 
software packages and books We 
believe that to make an intelligent pur- 
chasing decision you need as much 
information as possible) You need 
more than can fit into a short ad You 
need screen photos of software. not 
just a glowing description You need 
technical details about peripherals 

Youll find this kind of detail in our 
new 48-page catalog Its unique in the 
small computer field Best of all. its 
FREE 


Peripherals Plus 


119 Maple Ave . Morristown. NJ 07960 


31 


4K ROM 
1K RAM 


Tee e 


Sep, 
eh 
wil4 
=P Se 


Kai TO 8 
Ga PKABS (Ke5) 
Fang 

G=1 TO 4 

Nae 

LET FPeFP+RND (7) -4 
FOR d=1 TO 4 

LET N=N-+ 4 

LET PeF+RND C7) 4 
IF Ped THEN LET 

IF Pig? THEN LET 
IF PS THEN LET 

IE Pe’ THEN LET 

IF Fe THEN LET Pkt 
IF Pag THEN LET P= 

IF P=? THEN LET | 
IF Peli THEN LET P=P+] 
Ir Pei THEN LET Per) 
IF Pai THEN LET Pepel 
IF Pelé THEN LET Pert 
IF Pei? THEN LET Pere d 
IF Pei8 THEN LET Pept 
GUSUB 497+Fx5 

NEXT J 


FOR 
LET 
LET 


Das C7) 
Ess PAPND (LZ) 


SHEI 


Robot Composer 


Cecil Bridges 


As Richard Forsen has noted (S YNC 2:34), a series of tones 
can be generated by a series of FOR-NEXT loops. However, 
we are not accustomed to hearing this pitch scale of tones, 
and the duration of the tones varies inversely with the pitch. 
The Robot Composer corrects these deficiencies in this pitch 
scale and generates rhythmic, melodic tunes. 

The series of FOR-NEXT loops used to generate tones 
occupies lines 500 to 559. Each of these loops has a multiplier 
for N which corrects the tendency for low notes to be longer. 
The basic unit of duration, N, is set by line 100. Most of the 
remainder of the program is used to select the pitch, P, from 
the tone generator. Because some tones made by the generator 
are not notes in the familiar diatonic scale, lines 418 to 428 
skip such tones. The FOR-NEXT loops corresponding to 
these skipped tones are spacers and are necessary for the 
generation of the remaining tones in the diatonic scale. Lines 
402 and 405 bounce the pitch off the top and bottom of the 
scale if the limits of the scale are exceeded. 

Lines 5, 10, and 490 set the length of the tune and the value 
of S, an additive variable for the pitch scale, P. The variable S 
first drops in value and then rises again towards the end of the 
tune. Because high values of P are associated with low notes, 
and vice versa, the pitch will initially rise and then fall. 


Cecil Bridges, 1248 N. Denver, Tulsa, OK 74106. 


FOR 


NEXT G ~18 


NEXT K 
GOTO 5 
FOR I=] 
NEXT 1 
RETURN 
FOR I=1 
NEXT 1 
RETURN 
FOR Isi 
NEXT I 
RETURN 
FOR I=1 
NEXT 1 
RETURN 
FOR I=1 
NEXT I 
RETURN 
FOR I=1 
NEXT I 
RETURN 


TO 


TO 


TO 


1 A3 


1 ASN 


KA AV 


(REI 


1ixN 


LixN 


FOR I=1 TO 
NEXT I 
RETURN 
FOR Li 
NEXT I 
RETURN 
FOR Lei TO 
NEXT I 
RETURN 
FOR Li 
NEXT I 
RETURN 
FOR It TO 
NEXT I 
RETURN 
a Ken 
NEXT 1 
RETURN 
FOR =i TO 
NEXT I 
RETURN 


TO 


LOXN nt le 


LOXN 


Tass? 
MEX T I 
RE TURN 
FOR 


L=] 


TO Gah 


TO) GaN 


AA NEXT I 
200 RETURN 
Séi v4 FOR T=i TO GSM 


FKN 


J46 MEXT I 
SAF RETURN 


20) 


FOR Lei 
MEAT I 


TO BN 


J0 RETURN 

GEI wi FOR Isi TO Ox 
wide NEXT I 
woo RETURN 

TO Sah wet FOR T=1 TO XN 
eo NEXT I 
26 RETURN 

SESE 327 FOR Isi TO 7XN 
we NEXT I 
oa? RETURN 


SYNC Magazine 


Lines 20 and 150 set the length of melodic 
phrases within the tune and determine 
within phrases the pitch increment and 
variability of the pitch transition from 
one measure to the next. Lines 200 to 400 
determine length and rhythmic composition 
of the measures, as well as the average 
pitch increment and variability from one 
note to the other. 

In the program as presented, pitch tends 
to stay generally within the limits of the 
pitch scale; small changes can be made in 
the additive variables in lines 150 and 
400, but if large changes are made, the 
pitch will constantly bounce off the scale 
limits causing the music to be less interest- 
ing. A rising pitch in measures may be 
produced by changing the -4 in line 150 to 
a -5, and a -3 will produce a pitch decrement 
between phrases. Substituting a -5 for -4 
in line 400 will produce a rise in pitch 
within measures and -3 will produce a 
decrement. Of course, pitch increments 
in phrases can be combined with decre- 
ments in measures or vice versa. 

Other functions can be substituted for 
line 10: 

10 LET S=-1+(K-5)*(K-5) 

produces a more rapid initial rise and 
more rapid decline than the original line 
10. By subtracting these functions from a 
constant, they may be inverted. By chang- 
ing K, G, and J, the length of tune, phrase, 
and measure can be changed. You will 
have to make corresponding changes to 
lines within the FOR-NEXT loops. 


Rhythm may be changed by modifying 


lines 100, 200, and 205. For instance: 


100 LET N=6 
200 FOR J=1 TO 4 
205 LET N=N-1 


produces a happy rhythm. A drum roll 
sound will be produced at the end of each 
measure if the limit of J is greater than N. 
A wide variety of rhythms is possible using 
these two examples and changing the values 
in lines 100 and 205 and the limit in line 
200. 

To produce only a single tune, line 498 
may be omitted. 

If a piece of insulated wire is laid under 
the computer and attached to the antenna 
of an FM radio, the sound will be trans- 
mitted without static to the FM receiver. 
You can now play your music through a 
high quality music system. 

Make changes cautiously, trying out 
the program between small changes; even 
renumbering seems to have an effect on 
tone quality, and introducing more compli- 
cated functions seems to make the sound 
unpleasantly “fuzzy.” If you attempt to 
lengthen the pitch scale, you will change 
the frequencies of all the notes; and you 
will no longer have a diatonic scale. A 
longer pitch scale is possible, but it is 
necessary to shorten the rest of the program 
to get it into 1K. wv 


September/October 


The most complex computer circuit can be 
explained with just nine cents 


The “penny switch.” It sounds strange. 
But it’s not. 

Joe Weisbecker, the designer of the RCA 
1802 microcomputer, was trying to explain 
to some children just how a computer works. 
He wasn't having much success. 


Computers Arent Magic 


Joe's hobby is magic. He thought, “maybe 
| can use some kind of illusion to show how 
a computer works.” But he didn’t really want 
to use an illusion. He didn’t want the chil- 
dren to think of a computer as magic. 

So he hit upon the idea of a simple flip- 
flop switch (the most common circuit in a 
computer) represented by the head or tail 
of a penny. This flip-flop circuit uses just 
one penny. Every time it receives an impulse 
it changes from head to tail or tail to head. 
Simple. 

But then Joe went on and put two of 
these simple flip flops together to make a 
Circuit that adds two numbers together. And 
another that subtracts numbers. Kids loved 
these circuits and played with them like 
games. 


Games With Pennies 


Before long, Joe devised circuits to play 
more complicated games like Tic Tac Toe, 


“Heads Up Game.” Starting with tails in all 
positions, how many times through to get 
all four pennies heads up? 


Guess A Number and Create A Pattern. 
Pretty soon he had 30 circuits (or games) 
that explained everything about computers 
from a basic adder to complex error correc- 
tion. The most complex circuit uses just 
nine pennies (or dimes for the big spender). 

These circuits, each one with a full size 
playing diagram, have been collected to- 
gether in a book called Computer Coin 
Games. With this book children or adults 
can easily understand the workings of even 
the most complex computer circuits. 


Games Magazine said, “whether or not 
you have any experience with computer 
technology, you'll be both amazed and de- 
lighted with the simplicity of the format and 
the complexity of the play. All you need is 
some common cents.” 

Dr. Dobbs Journal agreed, saying, “Com- 
puter Coin Games is a simple approach toa 
complicated concept. The book is liberally 
sprinkled with clever illustrations and dia- 
grams, and provides a relatively painless 
route to understanding how computer cir- 
Cuits function.” 


Money back Guarantee 


We're convinced that you'll understand 
the inner workings of a computer after playing 
these 30 games. If you don't, send the book 
back and we'll refund the complete price 
plus your postage to send it back. 

To order your copy of Computer Coin 
Games, just send $3.95 plus $2.00 for one, 
$3.00 for two or more for shipping and 
handling to Creative Computing Press, 
Morris Plains, NJ 07950. Visa, MasterCard 
and American Expess orders may be 

called toll free to 800-631-8112 (in NJ, 
201-540-0445). 

With its wonderful illustrations by Sunstone 
Graphics, Computer Coin Games makes an 
ideal gift. The Association for Educational 
Data Systems calls the book “an ideal intro- 
duction to the concepts of computer 
Circuitry.” 

Order your copy today. 


creative 
Gorepatirg 


Morris Plains, NJ 07950 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


33 


34 


4K(8K) ROM 
1K RAM 


Examining Prime Numbers: 
Two Programs 


George J. Repicky 


The prime numbers are a set of numbers 
which have as their distinguishing property 
the fact that they are divisible evenly only 
by themselves and one. Thus, 2, 3, 5, and 
7 are primes, whereas 4, 6, and 9 are not. 
While 1 would seem to fit the definition, 
it is not usually considered to be a prime. 

Aside from their own interesting prop- 
erty, mathematics teachers introduce prime 
numbers in the middle grades because 
they add a bit of puzzle-like fun to the 
class and because they provide an excellent 
vehicle for an introduction to factoring. 
They make an interesting subject for com- 
puters both because the testing of a number 
to see if it is a prime is an excellent 
application of the computer’s ability to 
perform many calculations rapidly and 
because they provide a good illustration 
of the use to which “IF...THEN” and 
“FOR...NEXT” statements can be put. 

The first of the two programs below 
tests a set of numbers to see which members 
of the set are primes. The program asks 
for (and enters with INPUT statements) 
the beginning and the end of the set, and 
displays those numbers in the chosen set 
which are primes. For example, if in 
response to the opening statement: 
ENTER STARTING NUMBER, 
you enter 20, and, if in response to the 
next statement: 

ENTER ENDING NUMBER, 

you enter 30, the result: 

THE PRIMES BETWEEN 20 AND 30 
ARE: 

23, 29 

will be displayed. 


George J. Repicky, 49 Roosevelt Ave., Schenec- 


tady, NY 12304. 


The second program produces the prime 
factorization of a selected number. The 
prime factorization of a number is the set 
of prime numbers which, when multiplied 
together, produce the number as their 
product. For example, the prime factors 
of 72 are 2, 2, 2, 3, and 3, since 2 X 2 X 2 
X 3 X 3 = 72. If, in response to the 
opening statement: 

ENTER A NUMBER BETWEEN 2 AND 
32,767 

you enter 72, the computer will display: 
THE PRIME FACTORS OF 72 ARE: 

ën, 2y Syne d 

If a prime number is selected for factori- 
zation, the computer will display this fact. 
If, for example, you entered the number 
73, the computer will display: 

73 IS A PRIME, AND HAS NO PRIME 
FACTORS EXCEPT ITSELF. 

In addition to producing their answers, 
both programs cycle again upon entering 
the number 1. The entering of any number 
other than 1 will stop the program. 

Both programs are written for the 4K 
ROM. Both can be entered together and 
will run on 1K RAM, although, if both 
programs are in the computer, you can 
run out of memory if you choose a partic- 
ularly wide range of values when running 
the first. To run the first program simply 
use the RUN command; to run the second 
program, you must enter RUN 1010. When 
running these programs for the first time 
it is a good idea to use a short range of 
values for the first or a low number for 
the second. Wide ranges or high values 
can take some time to run. Once you are 
sure the programs are running well, save 
them on tape, delete the second. If you 
plan to take a break, try a wide range (say 
M = 1, N = 500 or 1000). This will take 
many minutes to run! Fa 


SYNC Magazine 


Testing a Range of Numbers for Primes 


10 

20 

30 

40 

DO 

60 

ZO 

DO 

QQ 
100 
110 
120 
170 
140 
150 
160 
170 
180 
190 
ZOO 
210 
220 
230 
240 
2590 
260 
270 
28O 
290 
SOO 


CLS 

PRINT 
PRINT 
PRINT 


"ENTER STARTING NUMBER" 


INPUT M 


CLS 

PRINT 
PRINT 
PRINT 


"ENTER ENDING NUMBER" 


INFUT N 


CLS 

FRINT 
PRINT 
PRINT 
PRINT 
FRINT 
IF M=2 


"THE PRIMES BETWEEN#";M; "#AND#" 3 N 
"ARE: #" 


THEN PRINT "2,#"3 


FOR J=M TO N 
FOR K=2 TO J-i 


STOF 


LET. Q=J/K 
IF J=@xK THEN GO TO 240 

NEXT E 

PRINT Aen, än: 

NEXT J 

PRINT 

FRINT 

FRINT "TO TEST NEW NUMBERS, ENTER i" 
INFUT Z 

IF Z=1 THEN GO TO 10 


Note: If the 8K ROM is used, line 210 
must be replaced by something like: 
210 IF J=INT(Q)*K THEN GO TO 240 


Prime Factorization 


1010 CLS 

1020 FRINT 
1020 PRINT 
1040 PRINT 


2 AND 


1050 INFUT 
1960 CLS 

1070 FRINT 
1080 PRINT 
1090 IF N= 
1100 PRINT 


N; "HA 


1110 FOR J 
1120 LET Q 
1130 IF N-@QxJ=0 THEN GO SUB 1219 
1140 NEXT 

1150 CLS 

1160 FRINT 
1170 PRINT 
1180 FRINT 
HAS NO FRIME FACTORS 


EXCEP 


1190 PRINT 
1200 GO TO 
1210 PRINT 
1220 IF Q= 
1230 LET N=Q 
1240 LET J 


1260 FRINT 
1270 PRINT 
1280 PRINT 
1290 INFUT 
1300 IF A= 
1310 STOF 


"ENTER A NUMBER BETWEEN 
32,767" 
N 


2 THEN GO TO 1180 
"THE FRIME FACTORS OF#"; 
RE: #" 
=2 TO N/2 
=N/J 


J 


N "HIS A FRIME, AND 
T ITSELF" 

1280 

KTM Af 

1 THEN GO TO 1260 


=J~1 


1250 RETURN 


"TO TEST A NEW NUMBER, ENTER 1 
A 
1 THEN GO TO 1010 


Note: To run the program with 8K ROM, 
line 1130 must be changed to something 
like: 
1130 IF INT(Q)=Q THEN GO SUB 1210 


September/October 


20, 30 lower the display. 


530 accepts the starting number 
of the set to be tested. 
70., 80 lower the display. 


100 accepts the ending number of 
the set to be tested. 
120, 130 lower the display. 


170 insures that 2 will be displayed. 
180 presents each number in turn. 

190, 200 test each possible divisor; 
if a divisor is found, 2109 drops 

the number from further consideration. 
220 prints only those numbers found 
not to have a divisor. 


270 to 290 repeat the program 


Lowers display for neatness. 
Asks for number to be factored. 
Enters number to be factored. 
Lowers display. 

Identifies 2 as a prime number. 


Tests possible divisors. 
Defines the quotient. 


Identifies a divisor which has no remainder. 


Goes to next divisor. 
Lowers display. 


Displays and identifies a number 
if it is a prime 


Begin subroutines prints prime factor. 
Determines if all factors have been found. 
Factors out the divisor. 

Resets J to try the same factor. 


Presents option to rerun program. 


35 


Defuse Program Listing 


LO RANDOMISE 
20 LET @=RND C99) 

30 LET B=RND (99) 

40 LET C=RND (99) 

GO LET Des 

60 LET Ers 

70 LET Feo 

BO LET Sea 

90 CLS 

LOO PRINT ‘ORLIHBEAEHPH AA SE COND S445 I GNAL " 
110 PRINT 


(20 LET LsbEEE C1446.) Ccurremk line on Screen: 


L30 IF Lage THEN INFUT D 

140 IF pelo THEN PRINT "H? 

150 PRINT D; 

160 IE Lou THEN INPUT E 

170 IF Ecio THEN PRINT "Rm: 

180 PRINT CHR”; Es 

Loo IE LAZZ THEN INPUT F 

200 IF Fedo THEN PRINT "ab", 

S10 PRINT "HH sF, 5, LO (ABS (A-D) +488 (B-E) 
ABS (LF) E 

220 1F Gesi AND Be AND C=F THEN GO TO 270 

250 IF Se2o0 THEN GO TO S10 


240 TF Le4 THEN GO TO 30 (prevent screen over ti ow) 


250 LET SeS+10 
2460 GO YO Li 

270 CLS 

280 PRINT 

2590 PRINT “BOMB DEFUSED AT “5p” SECONDS" 
200 GO TO Zén 

210 CLS 

220 PRINT 

210 PRINT “BOOGRKMM THE BUTLEING BLEW UE" 
BAO PRINT 

SSO PRINT "THE BOME WAS AT "ronn, Vg Br Y, gE 
SAD FR LAT 

370 PRINT "FLAY AaG&aIne" 

290 INPUT A$ 

390 IF CODE (A$) s THEN RUN 


36 


Defuse 


Raymond Fowkes 


You are the Chief of Security in a major 
government building. You have just 
received a telephone message from a ter- 
rorist group claiming that they have planted 
a bomb somewhere in the building. Fortu- 
nately, you have the most sophisticated 
electronic detection equipment available. 
Your detector gives off a signal that gets 
stronger as you get closer to the bomb. 
However, the building is large — 100 stories 
high, 100 rooms long, and 100 rooms 
wide—and you are pressing a time limit 
of 200 seconds to find the bomb and defuse 
It. 

Starting at the bottom (0, 0, 0), you 
enter the coordinates of each room you 
want to test (length, width, height) in 
response to the reading from your 
detector. 

This program was adapted to the ZX80 
and to fit into 1K of RAM from More 
Basic Computer Games published by Crea- 
tive Computing. "a 


Raymond Fowkes, P.O. Box 336, Coalinga, CA 
93210. 


Sample Run 


L W H Seconds Signal 
0 0 0 6636 
40 0 10 6636 
20 40 20 8376 
20 60 30 8434 
20 32 40 8666 
8550 
60 8666 
70 9159 


N 
© 
Nn 
CH 
LA) Fe 
E ao oa EN © CN ECH © 
LP 
© 


BOMB DEFUSED AT 100 SECONDS 
PLAY AGAIN? 
wh 


SYNC Magazine 


Worth A 
Fortune 


Past issues of Creative Computing. What 
are they worth today? It varies. Toacollec- 
tor, Vol. 1, No. 1 is worth $7 or $8. To a 
scrap dealer, less than two cents. 

But we're not selling old back issues. 
We're ail out. 

On the other hand, you know that much 
of the content of Creative Computing is 
timeless. The Depth Charge program in 
Vol. 1, No. 1 is just as challenging today as 
the day it was written. Walter Koetke’s 
series of five articles on using computers in 
the classrom are as valid today as the day 
they first ppeared in print. And scores of 
people have written about obtaining re- 
prints of Don Piele’s classic problem- 
solving series. 


Our Mistake 


In our early growth years when we had 
5,000 and then 10,000 subscribers we 
couldn't imagine we would ever need more 
than 1000 extra copies for back issue sales. 
That's about what we printed extra. How- 
ever, by the time we were going into Vol- 
ume 3, we found our stocks of Volume 1 
issues virtually depleted. 


Our Solution 


So we selected the best material from 
Volume 1, edited it, put it together in book 
form and sold it for $8.95, about the same 


as the six individual issues. Nine months 
later, we did the same with Volume 2. Then 
a year and a half later we did it again with 
Volume 3. 

Most other magazines in a high tech- 
nology field like small computers find their 
contents are quickly out of date. However, 
because we've concentrated on applica- 
tions and software, our content retains its 
value for a much longer time. Our sub- 
scribers know this and retain their copies of 
Creative Computing long after they've dis- 
posed of the more hardware-oriented 
magazines. 

Now you can obtain the best material 
from the first three years of Creative Com- 
puting in book form and the next three 
years (minus four issues) in the original 
magazine form. 


Our Offer 


We have a unique special offer, so pay 
close attention to this paragraph. (Compu- 
ter types ought to be able to understand 
this). If you order any one item below, you 
pay the full price. If you order any two 
items, take a 5% discount from the total; any 
three, take a 10% discount: any four, take a 
15% discount, any five, take a 20% dis- 
count, and on all six take a whopping 25% 
discount from the total price. 


Best of Creative Computing-Vol 1 $8.95 
Best of Creative Computing-Vol 2 8.95 
Best of Creative Computing-Vol 3 8.95 
Volume 4 (Four issues) 6.00 
Volume 5 (Ten issues) 15.00 
Volume 6 (Twelve issues) 18.00 


Less discount (5% for two items, 10% for 
three, 15% for four, 20% for five, 25% for all 
six) Shipping ($2.00 USA, $5.00 foreign) 


We guarantee you'll never find a better 
value in computer applications reading 
matter. On average you're getting 128 
pages of solid information for each $1.00. If 
youre notcompletely satisfied after you've 
read them, send the books or magazines 
back to us and we'll refund your full pur- 
chase price plus the return postage. 


Greative 
corpatirg 


Morris Plains, NJ 07950 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


ARTICLES AND COMMENTARY 


Learning About Smalltalk — Goldeen 


Eclectic Programming Languages 


e Editorials 
Birth of a Magazine — Ahl 
A Computer in the Classroom? 
Is Breaking Into A Timesharing 
System A Crime? — Tagg 
Where Are We Going? — Ahl 
Computers in Education 
What's Wrong With the Little 
Red Schoolhouse? — Ahl 
How to Cope With Your Computer 3 
Recent Trends in Mathem>* se 
Curriculum Rese- 8 
CITALA: C- mg 
— How. 
EXPER GI 
Monty Pyt! 
IFIP Confer 
Transportal 
The Parable 
Technical Tr 
CONDUIT Do 
Statewide Po 
Expected Be 
Hard Core Cé 
PLATO IV Syst 
TICCIT System 
PLANIT The Po 
Careers 
A Computer Car 
Career Educator 
Key to Your Futur A) 
Profile of an Indu: 


Indiset- 


Applications : Eë 
Computers andthe Ah E ae ate 
Computer Simulate Wess? 
Weather Forecastin, ,pucations 
Relativity for Computers All Arithmetic 
Mr Spock's 7th Sense — Kibler 
Programming and Languages 
Structured Programming — Hoogendyk 
On Computer Languages — Ahl 
Toward A Human Computer 

Language — Cannara 


September/October 


A New Approach to Testing — 
Computer Impact on Society 
The Computer Threat to Society — Ahl 
Digital Calculators — Then and Now 
The Computer. Threat to Society? — 
Putting Teeth Into Privacy 
Legislation — Hastings 
` eaders at Privacy 
+ — Hastings 
ung in the Space Age — 
irer Looks at Data 
Fritze 
lic Attitudes Toward 


cet A a Exchange — 

oushnell — Todd 

Playing PONG to Win — Ahl 

Your Own Computer? — Ahl 

Introducing Computer Recreations 
Corp. — Todd, Guthrey 

Creative Computing Compendium 

Flying Buffalo — Loomis 

Compleat Computer Catalogue 

National Computers in Education 
Conference? 


Input Device? - Bork 
Round and Round They Go 
The $2.98 Computer Library - 
Personal Computers 
Russian Computing - Ahl 
Desk Calculator from Chi 
Microprocessors & Micrc 

The State of the Art - C 

' eLanguages and Program 
The Reactive Engine Pa 
About Computing - Chi 
David vs. 12 Goliaths - 
Sixth Chess Champior 
Beating the Game - TF 
Simulated Strategies í 

Reisman 
Beyond BASIC - Salı 
The Computer “Glas 

Teaching with AP! 
Creative Chess - Ko 
SNOBOL - Touretz 
A Smalltalk Airplar 

e Artificial and Extra 


— Ab 

‘onference 

vacy Should You Have — 
Ex-Social Security 

r — Campbell 

mputers — Malcolm 
agement Information 


criminal Justice 
elman 
> to the Computer 


2at Computer 


gs 
Non-Human Intell 
i aiii An Esoteric Ethic: 
| AND THINGS The Thinking Cor ` 


Primer on Artific! Í i 
Can Computers 
An Earonthe Ur | 
Communicatior 
The Cosmic Su. 


H 


Computer Literacy Quiz - 
A Fable - Spero 

Let Us First Make It - Taylor 
Some Thoughts - Lees 


The Magic of EF TS - Ahi 


ARTICLES AND COMMENTARY 


e Technology — Present and Future 
The Future of Computer Technology - 
Computing Power to the People 
Videodiscs — The Ultimate Computer 


eLiteracy, Philosophy, Opinion 
What ıs Computer Literacy - Moursund 
Moursund 


Information Anyone? - Griffith 
The Government Dinosaur - Winn 


e Computers in Education 
Instructional Computing in Schools - Ah/ 
Should the Computer Teach the 
Student, or Vice-versa? - Luehrmann 
The Art of Education: Blueprint fora 
Renaissance - Dwyer 
Computing at the University of Texas 
Computers in Secondary Schools - 1975 
Compyouter Fair - Thomas 
The Madness known as 


Every Person and the Computer 
Amateur Computing - Libes 

"or Store? You Gotta Be 
berts 


Ohana 


2 Computer on 


of 
Ahl 
ner 


nbol - Mueller 
oetry - Chisman 
AcCauley 
2r 


y 


1S. AND PROGRAMS 


ns 

Jzzles - Ahl 

Recreations 

nto A Lesson - Homer 
r 

i me - Yarbrough 


"ZS Ej ior Games - Rogers 
a >D 

. d Geometry 
The Mystic o. 2n - Dickens 
Magıc Squares on the Computer - Piele 
Non-Usual Mathematics - Reagan 
The World of Series - Reagan 
Change For A Dollar - Hess 
Sequences - Jessen 
Progression Problems - Reeves 


37 


8K ROM 
2K(1K) RAM 


100 
110 
120 
130 
140 
150 
160 
170 
180 
190 
ZOO 
210 
SOQ 
320 
400 
410 
420 

at) 
450 
440 
470 
480 
BOO 
220) 
520 
530 
S40) 
e e Al 
560 
570 
580 
S90 
600 


38 


The Great Circle Route 


Chuck Dawson 


REM "GREAT CIRCLE" 

FRINT "“DEFARTURE FOINT" 

GOSUB 400 

LET LATI=LATKXFI/180 

GOSUB 450 

LET LONG1=LONG 

PRINT "DESTINATION" 

GOUD 400 

LET LAT2Z=LATKPI/180 

GOSUB 450 

LET LONG2=LONG 

CLS 

LET D=(LONGi-LONGZ) XFI/180 

LET Z=SIN LATIXSIN LAT2+ (C085 LATI*COS LAT2*COS 
LET DIST=INT (.5+¢108000/FP1Ix*ACS Z)) 


PRINT AT 19,0; "DISTANCE#=#"; DIST/10; "#NAUTICAL MILES" 


PRINT "“OR#"s.11SkDIST;"#STATUTE MILES" 
STOF 

SAVE "GREAT CIRCLE" 

RUN 

PRINT "LATITUDE" 

GOSUB 300 

LET LAT=DEG+MIN/&60+SEC/3600 
RETURN 

PRINT "LONGITUDE" 

GOSUB Soo 

LET LONG=DEG+MIN/60+SEC/3400 
RETURN 

FRINT "INFUT DEGREES#"'; 
INPUT DEG 

PRINT DEG 

PRINT "INPUT MINUTES#"; 
INPUT MIN 

PRINT MIN 

FRINT "“INFUT SECONDS#"; 
INFUT SEC 

FRINT SEC 

PRINT 

RETURN 


D) 


For those who have the 8K ROM. “The 
Great Circle Route” shows something of 
its possibilities. After entering the program 
on your computer, enter the latitude and 
longitude of any two points in the world, 
and the computer will calculate and display 
the distance between them. This is the 
“great circle route.” The primary answer 
is in nautical miles, but this answer is 
converted to statute miles by line 200. 
Line 200 can be used to convert the answer 
to kilometers by changing the .115 multi- 
plication factor to .185035. The program 
requires 2K RAM but it may be usable on 
1K machines by using one letter names 
for the variables leaving out the seconds 
input portion, and omitting the conversion 
provision in line 200. 

When you enter a longitude east of 
Greenwich or a latitude south of the 
equator, use negative numbers. 

After years of looking up trig functions 
in tables, I am amazed by the speed at 
which this program runs. 


Chuck Dawson, 6520 Victoria, Fort Worth, TX 
76118. 


SYNC Magazine 


The ZX80/1 As Fortune Cookie 


H 
J) 


gK 


wl 


In addition to reputed oracular powers, 
the J Ching has proven to be a source of 
fascination for mathematicians and com- 
puter scientists. This ancient Chinese sys- 
tem of divination comprises one of the 
earliest known examples of a binary count- 
ing scheme. 

The I Ching |Book of Changes] uses 
solid and broken lines to construct curious 
little six-line figures or “hexagrams” like 
the one shown below: 


alt 


Since there are only two possible values 
for each of the six lines (solid/broken) it 
is not surprising that there are 64, or 2° 
hexagrams. 

Associated with each hexagram is a 
special interpretation based on the inter- 
relationship of solid and broken lines in 
the figure. This interpretation is believed 
to hold a particular relevance for the person 
for whom the hexagram has been con- 
structed. 


Craig Breighner, Present Time Systems, 1250 
Dagmar Ave., Pittsburgh, PA 15216. Program edited 
to 8K ROM by David Grosjean. 


September/October 


Craig Breighner 


There are several ways to construct an 
I Ching hexagram. Some methods use 
either milfoil or yarrow stalks. The stalks 
are hard to come by, so bamboo is often 
substituted. But the complexity of some 
of these methods—it is said that they can 
only be learned from a master—would 
seem to defy any kind of straightforward 
algorithmic definition (at least any that 
would fit into 1K of RAM). 

However, there are other methods. One 
is to use coins. This method has great 
popularity even in the Orient. A relatively 
simple version follows: 

1) Toss three coins simultaneously. 

2) Assign “point values” to the coins—2 
for heads; 3 for tails. 

3) Add up the total points for all three 
coins. 

4) If the total equals 6 or 8 draw a 
broken line (-— -). 

If the total equals 7 or 9 draw a solid line 
=] 

5) Repeat this procedure until six lines 
have been drawn, bottom to top. 

Now, this method can be readily simu- 
lated on the ZX80. The accompanying 
Basic program can be lots of fun at parties. 
And who knows? It may even hold a 
deeper significance for those who consider 
themselves to be particularly “in tune” 
with their machines. 

The program uses two nested FOR... 
NEXT... loops. The outer loop controls 
the number of lines in the hexagrams (6); 
the inner loop the number of coins (3) to 
be tossed. 

Unfortunately, the program does not 
tell the user what his or her hexagram 
means (What did you expect in IK, any- 
way?). But an excellent source of in-depth 
interpretations for each hexagram is 7 
Ching: Book of Changes, Causeway Books, 
New York. This is an inexpensive reprint 


8K ROM 
1K RAM 


of James Legge’s 1882 translation. It is 
still highly regarded both for its accuracy 
and its completeness. Because of Legge’s 
notoriety as an orientalist, this translation 
should be available at most large municipal 
and university libraries. 


100 DIM I(6) 

110 PRINT "DOES YOUR FUTURE LIE 
#IN HARMONY WITH THE"; 

120 Print "#ELECTRONIC PULSE OF 
# THEUNIVERSE?" 


130 PRINT 
140 PRINT "CONSULT THE ORACLE O 
F THE","I CHING: PRESS"; 


150 PRINT “#NEWLINE TO CREATEAN 
#I CHING HEXAGRAM." 

160 INPUT AS 

170 FOR J=1 TO 6 

180 LET K= 

190 FOR L=1 TO 3 

210 LET K=K+INT (RND*2)+1 
220 NEXT L 

230 LET I(7-J)=K 

240 NEXT J 

250 CLS 

260 PRINT "YOUR HEXAGRAM:" 
2/0 PRINT 

280 FOR J=1 TO 6 

290 LET K=I (J) 

300 IF K=4 OR K=6 OR K=8 THEN G 
OTO 330 

310 PRINT "me |! 

320 GOTO 34¢ 

330 PRINT "em (egen "` 

340 NEXT J 


Notes: 

310: Use the graphic on the 6 key 5 
times. 

330: Use the graphic on the 6 key 2 
times, space, 2 times. 


This program will work on 4K ROM 
with the following changes: 

210 LET K=K+RND(2)+1 

Use the graphic on the W key in lines 
310 and 330. ma 


39 


4K ROM 


2K(1K) RAM 4 angm an 


e ee ee EERE eee Hee eee 


The old game of Hangman can also be 
played on your ZX80. The program listed Raymond Fowkes 
below preserves not only the battle of 
wits between the two players, but also 
draws on the graphics capabilities of the 
ZX80 to draw the figure for you. The 
program with full prompts on the screen 
requires over 1K, but it can be played on 
IK by making the changes listed at the Sample Runs 3. 


end of the program. 1. HANGMAN 


After typing in your program, press RUN INPUT SECRET WORD. 
and NEWLINE. The first player then types “SOFTWARE” 


in a secret word of up to 17 characters. — ~---------------- 
After clearing the screen, the computer 

will indicate by dashes how many letters 2. 
the word has. The other player then 
attempts to guess the word by typing in 
letters most likely to be in the word. A 

right letter is placed in its correct posi- 
tion(s). A wrong or repeated letter is printed 

in the center of the screen and a body 

part is added to the figure on the gallows. 

The game ends when the figure is com- 
pleted or when the secret word is filled 

in. 


SECRET WORD: SOFTWARE 
INGCBMHPD (Player’s guesses) 
YOU GUESSED IT. 

THE WORD WAS: SOFTWARE 
PLAY AGAIN? 

SECRET WORD: -------- “YES” 


Raymond Fowkes, P.O. Box 336, Coalinga, CA 
93210. 


Hangman Program Listing Zo LET Bec 
370 FOR A=O TO Ext 
S60 IF COOE(C$)=A0GA) THEN GO SUB 
Än CA GO? 
a PRINT) "#EHANGMAN" 290 IF E=F THEN GO TO S50 
>20 FRINT 400 NEXT A 
40 PRINT 420 IF B THEN GO TO 350 
SO PRINT "INPUT SECRET WORD." 430 PRINT CHR (CODE (C)) rn: 
60 INPUT A$ 440 LET C=CODE (BE) | 
70 GLS 450 IF (>i THEN LET C#C-10 
BO PRINT "ann (6 shift T) 460 PORE Z4+APEEK (16594) +PEER (16597) 
FO PRINT "CRAACHRAAHAG (shift Gls shift A) £25640, 9 
LOG PRINT "RAD (shift Di shift oi 470 LET B$sTLE(BRE) 
L10 FOR Ä=1 TO 7 480 IF Dënn THEN GO TO 590 
120 PRINT CHAHHHEHRERA” (shift oi 490 GO TO 350 
130 NEXT À SOO POKE L43+PEER (16596) +PEEK (16397) 
140 PRINT “GAGGAAAGAGAA" (12 shift A) K256+A, CODE (CE) 


150 PRIN TSAR AAAS T (12 shift Gi ech fe | iy (IO) me | 


i 
6 Am STRT E 6 as ee ER This program may be converted for 1K 
bet PRALNI ad LET Fert) e 
17O PRINT San LET Bei by doing the following: 

IBO PRI NT PSE CRE T WORD a Heb" 540 RE i Delete lines 20-40 and 550-610 
orter ime.  # ° 3 JS PR Change line 620 to: 620 CLS 

ZUN KS vE fy 6 hall at 


Kee, ` Bes 
. % 
Po $ 
g "er 


qooneee 
ee! 


“£10 FOR E=0 TO 17 aO PRINT "YOU GUESSED IT." 


Zell IF Dës" THEN GO TO 310 woo GO TO GZ 


250 LET Be=TLs (Be) 610 PRINT “YOU LOSE. 
NEXT E b20 PRINT 

3 PERINY oO PRINT "THE WORD WAS. ds Ag 

D 

p Pe 660 PRINT PPLAY AGAIN?" 

ET pes #TZAGOSCLNUY" E70 INPUT A% 


FAIL) Cé öko [TF CODE CAB ag THE 


40 SYNC Magazine 


Binary dice? That sounds strange. What’s 
the point? 

Each binary die has six sides but instead 
of one to six spots, three sides have the 
numeral one and three have a zero. When 
rolled, the three dice, red, blue and green, 
produce a 3-bit binary number. 

The binary number can be easily converted 
to a decimal numbr. A binary 101 equals a 
decimal 5. After using these dice a few times, 
these conversions are quickly done even 
by 7 year olds. 


Designed for Understanding 


Binary dice are just one of many unique 
elements of the Computer Rage board game. 
The whole game is designed to help players 
easily understand the complexities of a large 
multiprocessing computer system while 
having great fun playing. 

Imagine you're using a large computer 
along with many other users. It’s Thursday 
and payroll checks have to be run. They 
have priority over your job. When this 
happens in the game you lose a turn. But 
then a vice president wants the results from 
the program you're working on—take another 
turn. Oh, oh, in your hurry, you make a 
program mistake. Too bad—return to the 
last checkpoint. 

Meanwhile one of your opponents, a fellow 
user of the computer, has heard from the 
president that one of his three programs 
has top priority; it advances to the output 
queue. But wait, on your next move you 
land on an “interrupt” and find that a brownout 
has just occurred, the computer has crashed, 
and all the programs of all players must 
return to the last checkpoint. 

The binary dice return to your opponent. 
He rolls 011, a four, and lands ona decision 


September/October 


High 
Roller 


Three binary dice add up to 
fast fun and easy winnings 


point. Rolling one die he gets a 1 which 
means he takes an 8-step flow intead of a 
16-step one. 

One it goes until one of the two to four 
players gets all of his programs to the output 
printer and wins. 


hag 


"TT BERRY DE oeng 


SHEERS Zou Lise 


Sets of three binary dice used in Computer 
Rage are available separately. 


Sturdy Components 


The game comes with a colorful, big 19” x 
19” playing board, 38 interrupt cards, 12 
miniature disk pack playing pieces (3 for 
each player) and 3 binary dice. Asupplement 
to the rules describes the way in which 
Computer Rage parallels a multiprocessing 
system. 

Computer Rage is designed for players 
from 7 to 14 years old but obviously can be 
played by adults as well. It is for two to four 
players. Many schools use the game along 
with a book such as Be A Computer Literate 
in computer literacy units for Grades 3 to 8. 
It's also an excellent game to have available 
in open or alternative classrooms. 


Discounts Available 


In fact we feel so strongly that Computer 
Rage should be in every school that we're 
offering a special discount to schools and 
to people who buy a game for a school. 

The price of one game is $8.95 postpaid. 
Buy one game for your family and another 
for a school and the total price is just $14.00 
postpaid (and $8.95 is tax deductible). 
Individuals or schools buying five or more 
games may take a whopping 50% discount— 
just $4.50 each. Customers outside of the 
U.S. must add $2.00 additional postage per 
game. 

If you'd like an extra set of three binary 
dice for home or classroom, they are available 
for just $1.25 per set or five sets for $5.00. 

Order today at no risk. If you’re not com- 
pletely satisfied, return the game or dice 
for a full refund. To order, send your check 
or charge card number to the address below. 
Visa, MasterCard, and American Express 
Orders may be called in toll-free to 800- 
631-8112 (in NJ 201-540-0445). School 
purchase orders should add an additional 
$1.00 billing fee. 

Don't put it off. Order this entertaining 
and educational game today. 


creative 
GCorpatirg 


Morris Plains, NJ 07950 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


41 


Test your skill and luck on a ZX80 
motorcycle! In this game you compete 
with another rider on a 32 mile track on 
which you meet various obstacles and 
road conditions. The key to winning the 
race is meeting the obstacles with just the 
right speed. The faster you try to go, the 
less chance you have of overcoming the 
obstacle. If you go too fast, you will go 
down; if you choose the right speed, you 
will advance after the obstacle according 
to the speed you choose. Of course, you 
cannot play it safe by sticking to the lower 
speeds because your opponent will beat 
you to the finish line. You must take the 
risks to win. No trophies are offered, but 
you can still be the winner. 

Type in the program and run it. The 
computer will print out a symbolic track 
and show the relative positions of the 
cycles as the challenges of the track are 
met. The first player will be asked how 
fast he wants to take obstacle #1 then 
presses a number from 1 to 9 and NEW- 
LINE. The second player is asked how 
fast he wants to take obstacle #1. He also 
enters his choice. After NEWLINE is 
pressed, the computer will show the posi- 
tions of the motorcycles according to the 
players’ choices. It will print how far each 
cycle advances and in parentheses the 
total miles travelled. If the cycle goes too 
fast, it will be down. A new obstacle is 
presented, and each player is asked how 
fast he wants to go to meet it. The play 
continues until one cycle (or both) com- 
pletes the 32 mile course and the winner 
declared. 


Richard Van Workum, 920 Leslie Ln., Hanford, 
CA 93230. 


42 


Sample Run 


GRAY CYCLE 
= 


BLACK CYCLE 


FALLEN RIDER 
HOW FAST? 


GRAY CYCLE INPUT 1 TO 9 
S 


Figure 1. First player’s turn. 


GRAY CYCLE 


BLACK CYCLE 


FALLEN RIDER 
HOW FAST? 


GRAY CYCLE INPUT 1 TO 9 
BLACK CYCLE INPUT 1 TO 9 
LS 


Figure 2. Second player’s turn. 


GRAY CYCLE 


BLACK CYCLE 


GRAY CYCLE ADVANCES 4 
BLACK CYCLE ADVANCES 3 


(5 MI.) 
(4 MI.) 


LOOSE GRAVEL 
HOW FAST? 


GRAY CYCLE INPUT 1 TO 9 


LS 


Figure 3. Race status after first turns. 


Motorcycle Race Game 


Richard Van Workum 


2 LET G=1 

3 LET Bel 
12 LET A$="BLACK CYCLE" 
14 LET BS="'"GRAY CYCLE" 


15 


GO SUB 815 


100 LET D=RND(6) 


104 


IF D=1 THEN PRINT "WATER AN 


D MUD" 


106 
pu 
108 
RN" 
110 
ACK" 
112 
IDER" 
114 
AVEL" 
120 
133 
140 
152 
IK 
156 
167 
170 
180 
181 
182 
185 
200 
210 


IF D=2 THEN PRINT "DEEP HOL 


IF D=3 THEN PRINT "SHARP TU 


IF D=4 THEN PRINT "“BUMPY TR 


IF D=5 THEN PRINT "FALLEN R 


IF D=6 THEN PRINT "LOOSE GR 
PRINT "HOW FAST?" 

PRINT 

LET D=RND(10) 

PRINT B$;" INPUT 1# TO 9" 
INPUT K 

PRINT 

PRINT A$;" INPUT 1# TO 9" 
INPUT U 

IF NOT K>D THEN LET G=G+tK 
IF NOT U>D THEN LET B=B+U 
IF G>32 THEN LET G=32 

IF B>32 THEN LET B=32 

GO SUB 815 

IF NOT K>D THEN PRINT BS;"'# 


ADVANCES#"3K,"('"'3G3"#MI.)" 


220 
OWN" , 
230 


IF K>D THEN PRINT B$;"#IS D 
II ("3 G3"#MI RE Ge 
IF NOT U>D THEN PRINT AS;"# 


ADVANCES#"3U,"("'3B3""#MI.)" 


240 
OWN" N 
242 
245 
90 
260 
280 
285 


310 
815 
845 
850 
860 


IF U>D THEN PRINT AS$;"#IS D 
"(":B;"#MI.)" 

PRINT 

IF G<32 AND B<32 THEN GO TO 


GO SUB 815 
IF G=B THEN PRINT ,"TIE" 
IF Cap THEN PRINT ,B$;"#WON 


IF B>G THEN PRINT ,A$;"#WON 


STOP 

CLS 

PRINT B$ 

GO SUB 880 

POKE PEEK(16396)+PEEK(16397 


)*256+11+G6,139 


870 
880 
885 
890 
895 


PRINT AS 

FOR S=1 TO 32 

PRINT "W"; (shift) 

NEXT S 

POKE PEEK(16396)+PEEK (16397 


}*2564574+B, 128 


900 
901 
905 


PRINT 
PRINT 
RETURN 


SYNC Magazine 


creative 
corpatirg 


Creative Computing-- Albert Einstein in 
black on a red denim-look shirt with red 
neckband and cuffs. 


\\ I'd rather 
SS. , be playing 
Pe, Spacewar! 


ld rather be playing spacewar-- black 
with white spaceships and lettering. 


Computer Bum-- black design by car- 


toonist Monte Wolverton on gray 
denim-look shirt with black neckband 
and cuffs. 


September/October 


Creative’s own outrageous Bionic Toad 
in dark blue on a light blue shirt for 
kids and adults. 


Give your 
tie a rest! 


All T-shirts are available in adult sizes 
S,M,L,XL. Bionic Toad, Program Bug and 
Spacewar also available in children’s sizes 
S(6-8), M( 10-12) and L(14-16). Made in USA. 
$6.00 each plus 75¢ shipping. 

Specify design and size and send payment 
to Creative Computing, 39 E. Hanover Ave., 
Morris Plains, NU 07950. Orders for two ar 
more shirts may be charged to Visa, Master- 
Card or American Express. Save time and 
call toll-free 800-631-8112 (in NJ 201-540- 
0445). 


Py 
(i 
S e F N 
$ a K SKS 
/ f bw ON £ ës, ` 
b A e Ki 
= $ E À "xv 
SC N BA R 
\ IS DW? = 
z E i J 
; k N IE E R > 
b A È: a $ 27 
AoA’ G D = / oy 2. 
4 E a j WË =: 
Li Zz Y 5 Ş 
A Hy d RE = 2 Kä 
SA ` ES Gs SJ 
SE E ty wei 
\ i = AN i 
y ) 


Beware the 
Program BUG! 


from Katie and the Computer 


The Program Bug that terrorized Cyber- 
nia in Katie and the Computer is back 
on this beige t-shirt with purple design. 
You can share the little monster with 
your favorite kid. 


TEET TT TTT ITT TIT T1777 7171 7T 


3 333333334333344 
339432342 Asz2: 


Plotter display of Pi to 625 Places in 
dark brown on a tan shirt. 


Crash Cursor and Sync from the comic strip 
in SYNC magazine emblazoned in white on 
this black shirt. 


little 
black Robot Rabbit (on a bright orange 


Roll down the block with this 


t-shirt) on your back and you can 
intimidate every carrot, radish or cuke 
in your way. 


43 


Software Review 


Hints & Tips For The ZX81 


Martin Wren-Hilton 


Hints & Tips for the ZX81 by Andrew 
Hewson is excellent for the average ZX81 
user who has little, or no knowledge of 
Z80 Machine Code programming, but 
would like to learn. There are sections on 
saving space in programs, understanding 
the Display File, converting ZX80 programs 
for use on the ZX81, how to let two or 
more programs access one lot of data and 
finally, 26 pages on Machine Code pro- 
gramming. 

The book begins by showing the reader 
how to save a considerable amount of 
RAM by carefully designing programs. 
With so much memory used for system 
variables, this chapter is essential reading 
for ZX81 users with only 1K RAM. 

The second chapter deals with the Dis- 
play File—showing how TAB, AT, PLOT 
and UNPLOT work. This chapter also 
details how the Display File can be used 
as Memory. 

The next section discusses the similarities 
and differences between the ZX80 and 
ZX81 and how to convert programs 
between the two machines. Two conversion 
charts are given—one for converting char- 
acter codes from ZX80 to ZX81, the other 
compares the Z X80 system variables with 
their ZX81 equivalents. 

Chapter four demonstrates how two or 
more programs can share one lot of data 
by transferring the data into RAMTOP 
before loading the next program. This 
technique also allows for data to be ‘NEW- 
proofed’ in a way in which the data can 
be subsequently retrieved and processed 
by another program. 


Martin Wren-Hilton, 4 Little Poulton Lane, Poulton- 


le-Fylde, Blackpool, FY6 7ET, England. 


44 


The final chapter explains to the com- 
plete novice how to write, load, edit, save, 
and debug Z80 Machine Language pro- 
grams. The reader is first introduced to 
the concept of bits, bytes, addresses and 
hexadecimal numbering. 

The author goes on to describe the 
Z80A registers, their relative uses, and 
the Z80A instruction set. Obviously, a 


book of this size cannot provide a full 


examination of the machine code of the 
Z80A microprocessor, but it does introduce 
the beginner to many basic concepts. 
Hints & Tips for the ZX81 ends with 
thirteen programs for the basic, 
unexpanded ZX81. These programs include 
a useful Hex Loader/Printer, a Line Renum- 


ber program which neatens programs but 


does not include GOTO or GOSUB renum- 
ber, five games, a machine code clock 
program, a statistics program which gen- 
erates the mean, standard deviation, inter- 
cept and slope of a given set of data. 

Hints & Tips is clearly typeset, but is 
only bound with a couple of staples. It is 
a very good value for the money and will 
introduce many to the complex world of 
machine code programming. 

Hints & Tips for the ZX81 by Andrew 
Hewson from: Hewson Consultants, 7 
Grahame Close, Blewbury, Oxfordshire, 
OX11 9QE England. 76 pp. softbound; 
£4.95. De 


The “QS Sound 
Board” For 
The ZX80/81 


Play tunes in three-part harmony on 
your ZX80 or ZX81! Based on the 
extremely versatile A Y-3-8910 sound gen- 
erator chip, the QS Sound Board features 
complete software control of the frequency 
and amplitude of three independent output 
channels as well as an envelope shaper 
and noise channel. 

The QS Sound Board can produce fairly 
accurate scales over a 5 octave range, 
from C at 32.7Hz to B at 989Hz with a 
minimal error of +/-0.5%. Because of the 
limitations of the power supply, no amplifier 
or speaker has been fitted to the QS Sound 
Board. Instead, the three channels have 
been mixed together and taken to a 3.5mm 
jack socket via a preset volume control, 
therefore an external amplifier and speaker 
are needed. The Radio Shack 277-1008 is 
recommended. 

If you wish to use more than the onboard 
memory with the QS Sound Board, you 
will need the QS Motherboard which allows 
the 16K RAM pack to be used in con- 
junction with the QS Sound Board and 
one other board. 

The QS Sound Board also features two 
8 bit input/output ports taken to a 16 pin 
i/c socket for easy connection to external 
control functions via ribbon cable. 

The prices for the above products are: 


QS Sound Board............... 
QS Motherboard............... £13.00 
OS Sound Board & Motherboard .£38.00 


Quicksilva are at 95 Upper Brownhill Road, 
Maybush, Southampton, Hants., England. 


SYNC Magazine 


4K ROM 


ZX81 Hardware Review (UK) 


Producer 1 2 3 4 5 6 7 8 
48K RAM pack . 148.35 ; ` 
16K RAM pack 36.99 54.05 49.95 Er? i his 
8K RAM pack ; 33.95 ; 
Se Ge pack E 12.9 1 6.25 This column will feature short programs 
S me Sec 28 00 U/D to show off your ZX80, impress your family 
KE SES 75,00 34.50 and friends. and tickle your imagination 
Geen ' when SYNC arrives at your place. We 
invite your contributions. Address them 
S ge board ae U to SYNC. 39 E. Hanover Ave.. Morris 
ull-size . 
ad 24.95 27.74 Plains, NJ 07950. 
Disc drive U/D . Enter: 
Printer U/D 49.95 10 PRINT USR(722) 
20 LIST USR(722) 
Press RUN and NEWLINE. 
All Prices in £ Sterling. Hit RUBOUT and continue until only 


U/D - Under Development 


1) Quicksilva, 95 Upper Brownhill Road, Maybush, Southampton, Hants. 
2) dK’tronics, 23 Sussex Road, Gorleston-on-Sea, Gt. Yarmouth, Norfolk. 
3) Haven Hardware, 4 Asby Road, Asby, Workington, Cumbria. 

4) Macronics, 26 Spiers Close, Knowle, Solihull, W.Midlands, B93 9ES. 

5) Audio Computers, 87 Bournemouth Park Road, Southend-on-Sea, Essex. 


6) Memotech, 103 Walton Street, Oxford. 


7) Redditch Electronics, 21 Ferney Hill Avenue, Redditch, B97 4RU. 
8) Sinclair Research Ltd., 6 Kings Parade, Cambridge, CB2 1SN. RK 


the cursor is left on the screen. Note the 
effects 
While the cursor is visible, type in your 
name. 
Our thanks to: 
David Plumb 
34 Hillside Crescent 
Enfield, Middx. 
London EN2 OHR 
England Be 


A one-hour LP record of eight synthesizers may 
change your views about computer music forever 


Binary Beatles 


by David Ahi 


Computer music. Who needs it? It’s mostly 
boring beep, beep, beeps or wildly modern 
stuff. It’s certainly nothing you'd want to 
listen to more than once. That's what | thought 
about computer music and most of my friends 
agreed. 

In 1978 | entered Yankee Doodle Dandy 
into my Software Technology system just 
to be different. Dick Moberg heard of it and 
asked me to perform in the Philadelphia 
Computer Music Festival. | agreed expecting 
to be the only one with something out of 
the ordinary. | was wrong. 


Computer Accompanist 

Nine individuals and groups performed 
in the festival. There were the usual Bach 
pieces but even they were different. Gooitzen 
van der Wal performed the last movement 
of the 2nd Bach Suite in a unique way. He 
played the flute solo while using the computer 
as accompaniment. 

Then Dorothy Siegel did the same thing, 
playing the clarinet solo part of Wanhal’s 
Sonata in b flat. The audience went wild. 

Hal Chamberlin played Bache Tocatta 
and Fugue ind minor. But also with a differ- 
ence. He used a large computer before 
hand to “compute” the waveform of every 


September/October 


instrument playing every note. It took one 
hour of computation time for each two min- 
utes of playback time. The result could hardly 
be distinguished from the organ in the 
Hapsburg Cathedral. 

Don Schertz had a home brewed synthe- 
sizer truly mounted on a breadboard that 
allowed him to control 25 parameters of 
each note. It produced spectacular sounds 
in his arrangement of Red Wing. 


Singing Computer 


In 1962, D.H. Van Lenten at Bell Labora- 
tories produced the first talking computer. 
Bell engineers taught it to recite the soliloquy 
from Hamlet. Then they went one step further 
and taught it to sing Daisy both alone and 
accompanied by another computer. This 
was also performed at the festival. 

Yes, the Beatles were represented. Andrew 
Molda played Hey Jude on his COSMAC 
VIP system with a program called PIN-8 
(Play it Now). 


Superb Quality Recording 


All these pieces and twelve others were 
recorded with broadcast quality equipment. 
Because of audience noise, eight were re- 
recorded later in a studio. We then took 
these tapes to Tru-Tone, a top recording 


studio and cut a lacquer master. Ít was a 
long session since the recording engineers 
insisted upon analyzing the sound from every 
source and setting up the equilization curves 
accordingly. It took over 12 hours to produce 
a one-hour lacquer master. 

Finished recordings were then pressed 
on top-quality vinyl and inserted into liners 
and record jackets. These were then shrink 
wrapped in plastic for maximum protection. 
We guaranteee that every LP record is free 
from defects or we will replace it free of 
charge. 

The extensive descriptions of each of the 
eight synthesizers and the festival would 
not all fit on the jacket so we've included an 
extra sheet with each record. This entire 
package is mailed ina protective corrugated 
package to insure that it reaches you in 
mint condition. The cost is a modest $6.00 
postpaid in the U.S. and $7.00 foreign. Send 
order with payment or Visa, MasterCard or 
American Express number to Creative Com- 
puting, Morris Plains, NJ 07950. 

This 12” LP record of the Philadelphia 
Computer Music Festival contains one hour 
of eight computer music synthesizers that 
youll listen to over and over again. Order 
one today! 


Greative 
corpatirg 


Morris Plains, NJ 07950 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


45 


We introduce in this issue the “Kitchen SYNC” by 
Alan Groupe, Michael Tardiff, and Ivan Zatkovich. 
This is not a column on cooking with the ZX80/1 
(although conceivably that could be covered). Rather, 
the wide ranging interests of this trio are suggested. 
Furthermore, they are open to suggestion for topics 
you want to hear more about. We will pass along all 


requests. 


HitcCnensync = | 


Alan Groupe, Michael Tardiff, and Ivan Zatkovich 


Expression Evaluators 
at Work 


The three of us work for Digital Equip- 
ment Corporation, and, in the course of 
our work, we have unlimited access to a 
great number of large computers. Yet we 
each recently bought ZX80s. Why? 

We were warned that the ZX80 was a 
relatively tiny computer, almost a toy, 
with limited capabilities and a “very small” 
amount of memory. But it was the restric- 
tions and the limitations of the machine 
that interested us. The computers we use 
every day have millions of bytes of memory; 
operating systems occupy tens of thousands 
of bytes of memory; programs have all 
the RAM they need and more. There is 
comparatively little need to “economize” 
in writing software. When such a need 
arises, we talk of shrinking a 20K program 
to fit into 16K. We decided that it would 
be fun to see just how far a “little” machine 
could be pushed. 

Since then, we have become impressed 
with some of the features this compact 
machine does offer, and we would like to 
share some of our observationss and dis- 
coveries with you. 

One of the first unusual (to us) properties 
of the ZX80 version of Basic that we 
“discovered” is that anywhere you need 
to enter a number, you can enter an 
equation instead. Or, to put it more impres- 
sively, if less comprehensibly, the expression 
evaluator is called at each instance of a 
value-required context. 

What does that mean, and why is it 
good? 

If a computer language is to accept 
and solve equations, which we will call 
“expressions,” it must have the ability to 
take an expression as input and return a 
numeric value as output. This portion of 
the language is called the “expression evalu- 
ator.” 


46 


The expression evaluator first gets values 
for the variables in an expression and 
then performs the indicated arithmetic 
operations to end up with a single value. 
For example, enter the following commands 
into your ZX80 in the immediate mode 
(that is, without typing line numbers 
first). 


You should have seen an “8” at the top of 
your screen. When you entered the third 
statement, the expression evaluator looked 
in memory and found the value of A 
(which was 5) and the value of B (set to 3 
in the second LET statement), then added 
them together and filed the result under 
X. 

While normally the expression evaluator 
is only used to handle arithmetic state- 
ments, like LET; on the Sinclair machine 
it is used anywhere a number can be 
entered. For example, in a GO TO state- 
ment, you could insert an expression in 
place of the statement number of the GO 
TO. Instead of: 


GO TO 40 


you could write 


GO TO X+10 


If X equals 30, the expression evaluator 
would first search out the value of X, add 
30 and 10, and then “GO TO” the result: 
statement number 40. 

In a machine like the Z X80, it is not 
much trouble for Basic to use the expres- 
sion evaluator often, but it certainly can 
be very handy for us in writing programs. 

For an example, enter and run the 
following small program: 


10 INPUT LAST 
20 PRINT LAST 
30 GO TO 10 


When you are prompted for input, enter 
the number 3. The number 3 will appear 
on the screen. Enter an 11 and an 11 
appears. On lesser machines (like the TRS- 
80, etc.) this is all the program will do. 
But on the Sinclair, you have just written 
a simple calculator! Enter 3+9 and 12 
appears on the screen. 4*7 gives you a 28. 
In fact, you can even use the previous 
answer in an expression (assuming you 
have typed in at least one expression 
previously). Enter LAST-5 and the Sinclair 
responds with 23 (assuming you been 
entering all the examples). 

When you entered 3, the expression 
evaluator was used. It evaluated the expres- 
sion and returned the result (3), which 
was stored in the variable LAST. When 
you entered 4*7, the expression evaluator 
evaluated the expression to 28 which was 
stored in LAST. And when you entered 
LAST-5, the expression evaluator recalled 
the value for LAST (28), subtracted 5 
from it, and returned the result (23) which 
was stored in LAST. 

Another posible use of this technique 
is in the following rather crude telephone 
directory: 


10 PRINT “ALAN GROUPE” 

20 PRINT “ALANS ADDRESS” 

30 PRINT “ALANS PHONE” 

40 STOP 

50 PRINT “MICHAEL TARDIFF” 

60 PRINT “MICHAELS ADDRESS” 

70 PRINT “MICHAELS PHONE” 

80 STOP 

90 PRINT “IVAN ZATKOVICH” 
100 PRINT “IZZIES BAR AND GRILL” 
110 PRINT “IVANS PHONE” 
120 STOP 


Running this program by entering “RUN” 
is of little value, since it will always print 
only the first person’s information. So you 
must run the program with the GO TO 
command rather than the RUN command. 
If you want Alan’s information, you enter 
GO TO 10. If you want Ivan’s, you enter 
GO TO 90. 


SYNC Magazine 


This is all well and good, except that 
remembering the numbers is probably 
harder than remembering the addresses 
and phone numbers. However, after typing 
in the program, you can enter the following 
commands in immediate mode (that is, 
without typing line numbers first): 


LET GROUPE=10 
LET TARDIFF=50 
LET ZATKOVICH=90 


Now, if you want information on Ivan 
Zatkovich, you only need to enter GO 
TO ZATKOVICH. Again the expression 
evaluator is used. It determines that the 
variable ZATKOVICH has the value of 
90 and then GOes TO statement 90. When 
you Save a program on tape, the values of 
the variables are also saved; so when you 
load your telephone directory again you 
will not have to re-enter the LET state- 
ments. A word of warning though—the 
RUN command clears the values of all 
the variables. If you accidentally enter 
RUN, you will have to re-enter all the 
LET statements or LOAD the tape again. 

The expression evaluator will also work 
with strings as well as with numbers, 
although we do not see a use for this 
feature at the moment. Run the following 
program: 


10 INPUT A$ 
20 PRINT A$,CODE(AS) 
30 GO TO 10 


You will notice that the cursor appears 
on the screen between a pair of quotation 
marks(“”). Enter the letter A. On the screen 
will appear the letter A and the number 
38, which is the ZX80’s internal numeric 
code for representing the character A. 
Now, using the RUBOUT and arrow keys, 
rubout the two quotation marks. You will 
notice that the familiar syntax error symbol 
appears. This is because the INPUT state- 
ment is looking for a string, and strings 
are delimited by quotation marks. If you 
enter “A” (including the quotation marks) 
you will see that it is accepted, because 
“A” is a valid string no matter whether 
you typed the quotation marks or whether 
the machine did it for you. 

Certain internal functions of the ZX80 
(those whose names end in $, such as 
CHRS$), return strings as their outputs. As 
before, rubout the two quotation marks, 
but this time enter CHR$(38) (no quotation 
marks). Once again, the expression evalu- 
ator is used and evaluates the expression, 
returning the string “A” as its output. 
Since this is a valid string, it satisfies the 
INPUT statement and is accepted. 

Now it is up to you to figure out a use 
for this feature of the ZX80. Send your 
discoveries to SYNC. Be 


September/October 


Sourcebook 
of Ideas 


Many mathematics ideas can be better illustrated 
with a computer than with a text book. 


Consider Baseball cards. If there are 50 
cards in a set, how many packs of bubble 
gum must be purchased to obtain a complete 
set of players? Many students will guess 
over 1 million packs yet on average it's only 
329. 

The formula to solve this problem is not 
easy. The computer simulation is. Yet you 
as a teacher probably don't have time to 
devise programs to illustrate concepts like 
this. 

Between grades 1 and 12 there are 142 
mathematical concepts in which the com- 
puter can play an important role. Things 
like arithmetic practice, X-Y coordinates, 
proving geometic theorems, probability, 
compounding and computation of pi by 
inscribed polygons. 


Endorsed by NCTM 


The National Council of Teachers of 
Mathematics has strongly endorsed the use 
of computers in the classroom. Unfortunately 
most textbooks have not yet responded to 
this endorsement and do not include pro- 
grams or computer teaching techniques. 
You probably don't have the time to develop 
all these ideas either. What to do? 

For the past six years, Creative Computing 
magazine has been running two or three 
articles per issue written by math teachers. 
These are classroom proven, tested ideas 
complete with flowcharts, programs and 
sample runs. 

Teachers have been ordering back issues 
with those applications for years. However, 


many of these issues are now sold out or in 
very short supply. 

So we took the most popular 134 articles 
and applications and reprinted them in a 
giant 224-page book called Computers in 
Mathematics: A Sourcebook of Ideas. 


Ready-to-use-material 


This book contains pragmatic, ready to 
use, classroom tested ideas on everything 
from simply binary counting to advanced 
techniques like multiple regression analysis 
and differential equations. 

The book includes many activities that 
dont require a computer. And if you're 
considering expanding your computer 
facilities, you'll find a section on how to 
select a computer complete with an invalu- 
able microcomputer comparison chart. 

Another section presents over 250 
problems, puzzles, and programming ideas, 
more than are found i in most “problem collec- 
tion” books. 

Computers in Mathematics: A Sourcebook 
of Ideas is edited by David Ahl, one of the 
pioneers in computer education and the 
founder of Creative Computing. 

The book is not cheap. It costs $15.95. 
However if you were to order just half of the 
back issues from which articles were drawn, 
they would cost you over $30. 


Satisfaction Guaranteed 


If you are teaching mathematics in any 
grade between 1 and 12, we're convinced 
you ll find this book of tremendous value. If, 
after receiving it and using it for 30 days 
youdo not agree, you may return it fora full 
refund plus your return postage. 

To order, send your check for $15.95 
plus $1.00 postage and handling to Creative 
Computing Press, Morris Plains, NU 07950. 
Visa, MasterCard, and American Express 
orders may be called in toll-free to 800- 
631-8112 (in NJ 201-540-0445). School 
purchase orders should add an additional 
$1.00 billing fee for a total of $17.95. 

Don't put it off. Order this valuable source- 
book today. 


creative 
Gorepatirg 


Morris Plains, NJ 07950 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


47 


eSources č č o =< = — CO. 


Software 


e Exclusive distributors for the ZX80/1 
technical documentation. ZX80/1 infor- 
mation, software, accessories, etc. Send 
for a free catalog to: 

The ZX-GROUP 
25 Shute Path 
Newton, MA 02159 


e Free ZX80 game software. 
Just send your original 8K ROM software 
as listings or on tape and I will send 
you an equal number of mine. 
Ken Wogaman 
P.O. Box 125 
Somerville, OH 45064 


e ZX80/MicroAce Users! 

1K — Computerized Cowboy, Assassin, 
Energy Costs, Home Inventory, Phone 
Number Organizer, and more! 
16K-French Vocab., Deluxe Computer- 
ized Cowboy. 
Send SASE for more info. 1K—$5 (2 
for $9); larger programs—$10 (2 for 
$17). Send to: 

Steven Karash 

ZX Software 

11 Holland Lane 

New Paltz, NY 12561 


e ZX80 Chess developed specifically for 
the ZX80. 3 levels of play against the 
computer; graphics board displayed; 
fairly rapid response time. $19 from: 

Z X80 Chess (American) 
P. Joy 
130 Rush Green Road 
Essex, RM7 0QA 
England 
Ask for details on other software; SAE. 


Program Techniques: Machine Lan- 
guage, Sorting, others. Educ.: Math 
(+-x/), Hi Prec. Div., Hex/Dec Conv., 
Pound Dollar Conv., Temp. Conv., 
Graphing, others. Games: Submarine, 
Craps, Lunar Lndr, others. $4.95 ea; 
any 3 $12; all 1K; check or money 
order to: 

The Italian Connection 

869 Levitt Pkwy 

Rockledge, FL 32955 


e Fascinating Life Graphics program; 
22x27 world; half second between dis- 
plays. 4K ROM; 1K RAM. $1 for list- 
ing, instructions, and patterns to: 

Jon T. Passler 
344 Cabot St 
Beverly, MA 01915 


48 


e ZXCHESS and Adventure ‘A’ in 4K or 


8K ROM; 16K RAM. Machine code. 
6 levels of chess against the ZX80/1; 
algebraic notation; displays normal video 
for white; inverse, black. £10 UK; $25 
US; incl. shipment to US. 
Adventure ‘A’ A search for your space 
ship to escape a hostile planet. First in 
a series. £7 UK: $20 US incl. shipment 
to US. 

Artic Computing 

396 James Reckitt Avenue 

Hull, North Humberside 

United Kingdom 


Hardware 


e Remote Switched Isolators. 
3 sockets each capable of 1KW load. 
Prices start at $79.95. For details: 
Electronic Specialists, Inc. 
171 S. Main St. 
Natick, MA 01760 
Phone: (617) 655-1532 


8K/4K ROM switch kit. 
Allows switch selection of ROMs. $24.95. 
Cassette load AGC/audio monitor; key- 
board beeper option; add $10.00 to basic 
switch kit price. 

Marex Electronics 

2805 Abbeyville Rd. 

Valley City, OH 44280 


Overvoltage protector, Model OV-1. 
A plug-on unit that saves your ICs if 
regulator fails. Also has computer on/off 
switch & allows operation on 115 v. AC 
or 12 v. DC. $35 + $2 shipping. 
USA only. 

Quest Research Associates 

P.O. Box 3073 

San Jose, CA 95156-3073 


e 16K RAM Expansion plus power supply, 
model MX-16, $89.95 + $3 shipping/ 
handling. Check or money order to: 

INSIGHT 

1889 Lewis Dr. 

Niles, MI 49120 
(or call 616-684-7868 for COD; no extra 
charge for COD) 


e 48K Memory Extension for ZX81. 
Allows ZX81 to run 48K Basic programs 
including up to 16K of assembly code. 
Z X81 sits on custom built case contain- 
ing the Memotech. £109 + 15% VAT 
kit form: £129 + VAT assembled. Send 
to: 

Memotech (Sales Dept.) 
103, Walton Street 
Oxford OX2 6EB 
England 


e ZX80/1 User Port. 

A small board allowing 8 independent 
input channels and 8 output channels, 
directly controlled from Basic or machine 
code. Details on uses included in booklet. 
Complete kit—£11.50; booklet of appli- 
cations—£.40; suitable loudspeaker— 
£.80. Add VAT and P&P. 

Technomatic 

17 Burnley Rd., NW 10 

01 452 1500 

England 


e ZX Printer. £49.95 by mail order from: 
Sinclair Research Ltd 
6 Kings Parade 
Cambridge, CB2 1SN 
England 


e The 55 Key keyboard from Schultz 
Systems (SYNC 1:3) is no longer avail- 
able. Stocks are exhausted. 


User Groups 


e Bay Area ZX80 User Group 
2660 Las Aromas 
Oakland. CA 94611 


e ZX80/1 User Group within the Notting- 
ham Micro-Computer Club. Contact: 
G. E. Basford 
9 Holme Close 
The Pastures 
Woodborough 
Nottingham NG1 46 EX 
England jw 


SYNC Magazine 


| 


David Ahl, Founder and 
Publisher of Creative Computing 


You might think the term “creative com- 
puting” is a contradiction. How can some- 
thing as precise and logical as electronic 
computing possibly be creative? We think 
it can be. Consider the way computers are 
being used to create special effects in 
movies—image generation, coloring and 
computer-driven cameras and props. Oran 
electronic ‘sketchpad" for your home 
computer that adds animation, coloring 
and shading at your direction. How abouta 
computer simulation of an invasion of killer 
bees with you trying to find a way of keep- 
ing them under control? 


Beyond Our Dreams 


Computers are not creative per se. But 
the way in which they are used can be 
highly creative and imaginative. Five years 
ago when Creative Computing magazine 
first billed itself as “The number 1 maga- 
zine of computer applications and soft- 
ware, we had no idea how far that idea 
would take us. Today, these applications 
are becoming so broad, so all- 
encompassing that the computer field will 
soon include virtually everything! 

In light of this generality, we take ‘appli- 
cation to mean whatever can be done with 
computers, ought to be done with comput- 
ers or might be done with computers. That 
is the meat of Creative Computing. 

Alvin Toffler, author of Future Shock and 
The Third Wave says, “| read Creative Com- 
puting not only for information about how 
to make the most of my own equipment but 
to Keep an eye on how the whole field is 
emerging. 

Creative Computing, the company as 
well as the magazine, is uniquely light- 
hearted but also seriously interested in all 
aspects of computing. Ours is the maga- 
zine of software, graphics, games and sim- 
ulations for beginners and relaxing profes- 
sionals. We try to present the new and im- 
portant ideas of the field in a way that a 14- 
year old or a Cobol programmer can under- 
stand them. Things like text editing, social 


September/October 


A REMARKABLE MAGAZINE 


creative 


Gorepatirg 


“The beat covered by Creative Computing 
is one of the most important, explosive and 
fast-changing.” — Alvin Toffler 


simulations, control of household devices, 
animation and graphics, and communica- 
tions networks. 


Understandable Yet Challenging 


As the premier magazine for beginners, it 
is Our solemn responsibility to make what 
we publish comprehensible to the new- 
comer. That does not mean easy; our 
readers like to be challenged. It means 
providing the reader who has no prepar- 
ation with every possible means to seize 
the subject rnatter and make it his own. 

However, we don't want the experts in 
Our audience to be bored. So we try to 
publish articles of interest to beginners and 
experts at the same time. Ideally, we would 
like every piece to have instructional or 
informative content—and some depth— 
even when communicated humorously or 
playfully. Thus, our favorite kind of piece is 
acessible to the beginner, theoretically 
non-trivial, interesting on more than one 
level, and perhaps even humorous. 

David Gerrold of Star Trek fame says, 
“Creative Computing with its unpreten- 
tious, down-to-earth lucidity encourages 
the computer user to have fun. Creative 
Computing makes it possible for me to 
learn basic programming skills and use the 
computer better than any other source. 


Hard-hitting Evaluations 


At Creative Computing we obtain new 
computer systems, peripherals, and soft- 
ware as soon as they are announced. We 
put them through their paces in our Soft- 
ware Development Center and also in the 
environment for which they are intended — 
home, business, laboratory, or school. 

Our evaluations are unbiased and accur- 
ate. Wecompared word processing printers 
and found two losers among highly pro- 
moted makes. Conversely, we found one 
computer had far more than its advertised 
capability. Of 16 educational packages, 
only seven offered solid learning value. 


When we Say unbiased reviews we mean 


it. More than once, our honesty has cost us 
an advertiser—temporarily. But we feel 
that our first obligation is to our readers and 
that editorial excellence and integrity are 
our highest goals. 

Karl Zinn at the University of Michigan 
feels we are meeting these goals when he 
writes. “Creative Computing consistently 
provides value in articles, product reviews 
and systems comparisons...inamagazine 
that is fun to read.” 


Order Today 


To order your subscription to Creative 
Computing send payment to the appropri- 
ate address below. Customers in the 
continental U.S. may call toll-free to 
charge a subscription to Visa, MasterCard 
or American Express. 

Canada and 


Term USA Foreign Surface Foreign Air 
1 year $20 $29o0r £12.50 
2 years $37 $550r £24.00 $970r £41 
3 years $53 $80 or £34.50 


$50 or £ 21 


$143 or £ 61 
We guarantee your satisfaction or we 

will refund your entire subscription price. 
Join over 80,000 subscribers like Ann 


Lewin, Director of the Capital Children’s 
Museum who says, “I am very much im- 
pressed with Creative Computing. It is 
helping to demystify the computer. Its arti- 
cles are helpfu!, humorous and humane. 


The world needs Creative Computing.” 


Greative 
Gorepatirg 


P.O. Box 789-M 
Morristown, NJ 07960 
Toll-free 800-631-8112 
(In NJ 201-540-0445) 


27 Andrew Close, Stoke Golding 
Nuneaton CV13 6EL, England 


49 


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Brought to you by the people at 


creative Gorpatirg 


SYNC is the dynamite bi-monthly magazine for users of the Sinclair ZX80. The main 
focus is on applications, programming techniques, hints and tips for getting the most 
out of the ZX80. SYNC also reviews new peripherals, software and books for the ZX80. 

Subscriptions to SYNC cost just $10 for six bi-monthly issues (£10 in the U.K.). Send to 
SYNC, 39 E. Hanover Avenue, Morris Plains, NJ 07950, USA. 


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